The logos of Amazon, Apple, Facebook and Google are seen in a combination photo. Photograph:( Reuters )
Social media platforms are under particular scrutiny after US intelligence agencies said Russia used them to wage an influence operation to interfere with the 2016 election - a claim Moscow has denied
In the run-up to the 2020 presidential election, America's big tech companies are being challenged on many fronts from across the political spectrum, from antitrust concerns to their policies on political ads and ensuring election security.
Many of the Democratic presidential candidates have argued in favour of either breaking up or tightening regulation of firms such as Facebook Inc, Alphabet Inc’s Google and Amazon.com Inc.
Republican President Donald Trump's administration has also stepped up its scrutiny, announcing a wide-ranging investigation in July into whether major digital tech companies engaged in anti-competitive practices.
Trump's Democratic challengers also criticise online platforms for allowing politicians to make false claims in advertising ahead of the election next November.
Social media platforms are under particular scrutiny after US intelligence agencies said Russia used them to wage an influence operation to interfere with the 2016 election - a claim Moscow has denied.
Here are some of the candidates' positions on Big Tech.
Trump, whose social media use and digital advertising campaign helped propel him to the White House in 2016, in September attacked the "immense power" of social media giants in his address to the United Nations.
Trump has stopped short of calling for tech giants to be broken up, as Democratic Senators Elizabeth Warren and Bernie Sanders have, but said "obviously there is something going on in terms of monopoly," when asked about major tech companies in a June interview with CNBC.
Trump and other Republicans have also criticized social media companies, without evidence, for alleged political bias.
The president's eldest son, Donald Trump Jr. wrote an opinion piece for The Hill political website in September entitled "Free speech suppression online builds case to break up Big Tech."
Silicon Valley firms have also been at odds with the Trump administration over policies such as its repeal of Obama-era net neutrality rules and the impact of the U.S.-China trade war on their supply chains.
Biden, who was vice president in the Silicon Valley-friendly Obama administration, has taken a more moderate stance than his progressive rivals on the issue of big tech company break-ups.
In a May interview with the Associated Press, he said that splitting up companies such as Facebook was "something we should take a really hard look at" but that it was "premature" to make a final judgment.
The campaign told Reuters that, as president, Biden would aggressively use "all the tools available - including utilizing antitrust measures" to ensure corporations act responsibly.
He did not speak up during a discussion of the issue at the most recent Democratic debate in October.
Biden has criticized e-commerce giant Amazon's $0 federal tax bill in 2018.
"I have nothing against Amazon, but no company pulling in billions of dollars of profits should pay a lower tax rate than firefighters and teachers. We need to reward work, not just wealth," he said in a tweet in June.
His campaign also clashed with Facebook, Twitter and Google over their political ad policies after they refused to take down a Trump ad that the Biden team said contained false claims about his son Hunter's dealings with Ukraine.
Warren is leading the charge to break up big tech companies on the grounds they hold outsized influence and stifle competition.
She has called for legislation to restrict large tech platforms - which she would designate as "platform utilities" -from owning and participating in a marketplace at the same time.
Under this law, Apple would not be allowed to both run the App Store and sell its own apps on it, for example.
She also said she would nominate regulators to unwind anti-competitive mergers such as Facebook's deals for WhatsApp and Instagram, and Amazon's deal for Whole Foods.
Warren in October challenged Facebook's policy of exempting politicians' ads from fact-checking by running ads containing the false claim that CEO Mark Zuckerberg was endorsing Trump's re-election bid.
The senator from Massachusetts has also said that she would reject campaign donations over $200 from executives of big tech firms.
Sanders, a US senator from Vermont who frequently criticizes corporate influence, has also called for the break-up of big tech companies such as Facebook and Amazon.
His administration would "absolutely" try to split apart the companies, Sanders said at a Washington Post event in July.
He has said that he will have the Federal Trade Commission (FTC) review all mergers that have taken place during the Trump administration. His broad plan to reshape corporate America would also mandate all large companies to be owned partly by their workers.
Asked how he differentiates himself from Warren on major issues, Sanders told ABC in October: "Elizabeth considers herself - if I got the quote correctly - to be a capitalist to her bones. I don't."
Sanders has been vocal in his attacks on Amazon over issues such as its tax contributions and working conditions at its warehouses. In 2018, he introduced a 'Stop BEZOS Act' in the Senate, in a reference to Amazon CEO Jeff Bezos, which would make large corporations either pay their workers more or pay the government for public benefits that their workers receive.
In general, Pete Buttigieg, who became Facebook's 287th user shortly after it was launched in 2004 at Harvard University, where he was a student, has been more reluctant to slam the tech giants than some other candidates.
The mayor from South Bend, Indiana, said that the break-up of big tech companies is a "remedy that should be on the table," but also said it was not a politician's place to designate which companies should be broken up.
He has said that the FTC should be empowered to prevent and sometimes reverse mergers, but argued that large tech companies should be scrutinized for their actions rather than their size. He says concerns over monopolies and concerns over data security or privacy should not be conflated.
He is in favour of having legislation to protect individual data rights at a national level, including the right to be forgotten - which would give citizens the power to demand that online platforms delete data about them, as is the case in Europe.
Senator Harris of California, the home of Silicon Valley, has said that Facebook has not been sufficiently regulated. She has not called outright for the break-up of big tech firms but said it should be "seriously" considered.
During the campaign, Harris touted her experience protecting consumers' online privacy while she was state attorney general.
In Congress, Harris, along with fellow candidate Senator Amy Klobuchar, introduced the bipartisan ENOUGH Act in 2017 to protect against online exploitation of private images. Harris recently called on Twitter to suspend Trump's Twitter account, saying his tweets threaten violence. In response, the company said that Trump's tweets did not violate its policies.
The Minnesota senator has made oversight of big technology companies one of her major issues in Congress and argued for data privacy laws and net neutrality safeguards as priorities at her campaign launch in February. Klobuchar has called for tighter regulation of tech giants and suggested that companies who profit from users' data could be taxed.
She has not endorsed Warren's plan for their break-up, saying that she would first want investigations. Her plan for her first 100 days in office includes an "aggressive retrospective review of mergers," which she said she would pay for with an extra merger fee on "megamergers."
She is also one of the authors of the bipartisan Honest Ads Act, which would require social media platforms to disclose the purchaser of a political ad, as is required for television and print ads.
Yang, the former CEO of a start-up, has benefited from a surge of grassroots supporters on social media who style themselves as the #yanggang.
Although the technology entrepreneur said "we would be well served" if big tech companies were to break themselves up, he is more focused on dealing with the impact of automation on American jobs and on regulating artificial intelligence. Yang has also emphasized the negative effects of tech on mental health and said he would create a Department of Attention Economy, ideally led by tech ethics advocate Tristan Harris, to look at how to responsibly design and use apps and devices.
He has also called for people to receive a share of the economic value generated from their data.
New Jersey Senator Booker said that Warren's call to break up the tech giants was "more like a Donald Trump thing to say" and has instead argued that stronger antitrust laws need to be enforced.
When questioned at the October Democratic debate on the issue, Booker advocated reforms to stop tech companies being used "to undermine our democracy" around elections.
He talked broadly about antitrust, "from pharma to farms," but did not single out tech companies.
A Stanford University graduate who co-founded his own social media start-up WayWire, Booker has historically received donations from major Silicon Valley names such as Zuckerberg. The Facebook CEO also donated $100 million to Newark schools when Booker was mayor of the New Jersey city.
Beto O' Rourke
O'Rourke, a former US representative from Texas, wants to see Big Tech regulated rather than broken up. He has said he does not think it is the role of a president to designate which companies should be dismantled.
O'Rourke's campaign told Reuters he would stand up for small business by preventing online platform owners from promoting their own content and products over that of competitors. He also plans to create a new digital markets regulator to create and enforce rules on issues such as privacy and data mobility.
O’Rourke, who as a teenager was part of an influential hacking group, has also said he thinks social media companies should be treated as publishers.
He wants to amend Section 230 of the Communications Decency Act, which generally provides immunity to online platforms for content posted by users, to make social media companies more accountable for the amplification of hate speech and domestic terrorism on their platforms.
His campaign recently urged Facebook, Twitter and Google to do more to combat online disinformation, after the campaign encountered the spread of a false claim about a gunman in a mass shooting.
Castro, who was secretary of housing and urban development in the Obama administration, has said it is worth considering proposals to break up the big tech companies and said during the recent Democratic debate that the US needs to take a stronger stance in cracking down on monopolistic trade practices.
In the October debate, the former mayor of San Antonio, Texas, also singled out Amazon by name for helping to "put small businesses out of business" and for "shortchanging a lot of its workers."
Gabbard, a US representative from Hawaii, has called for the break-up of big tech companies and praised Warren's plan.
In July, she filed a $50 million lawsuit against Google accusing the company of discrimination when it temporarily suspended her ad account after the first Democratic debate. Google said the account had been automatically flagged for unusual activity, without specifying exactly what the issue was.
Gabbard said that Google's actions reflected "how the increasing dominance of big tech companies over our public discourse threatens our core American values."
California billionaire Steyer has said he is running for president to remove the influence of corporate money from politics.
In the October debate, he said that monopolies either have to be dismantled or regulated, but that to win against Trump, Democrats would have to "show the American people that we don't just know how to tax and have programs to break up companies."
Instead, he said, Democrats must harness the innovation and competition of the private sector.
Steyer's campaign has been noted for its massive ad spending which helped push him to the debate stage, including more than $6 million in Facebook ads, according to Democratic digital firm Bully Pulpit Interactive.