Hanna is retiring from the House and is not seeking re-election, leaving him more leeway to risk upsetting colleagues and voters over his break with Trump. Photograph: (AFP)
The break by Richard Hanna of New York followed days of uproar over Trump's criticism of the parents of a Muslim US Army officer
A Republican lawmaker in Congress became the first to break with the party and support Democrat Hillary Clinton for the White House on Tuesday amid signs of growing Republican unease with volatile presidential nominee Donald Trump.
The break by Representative Richard Hanna of New York followed days of uproar over Trump's criticism of the parents of a Muslim US Army officer killed in the Iraq war, which has fueled a fresh round of Republican rebukes of the New York businessman.
Illustrating the escalating tension between the candidate and the party, Trump pointedly thanked the primary opponent of Republican House of Representatives Speaker Paul Ryan on Monday for his "kind words" after Ryan had issued a statement saying the sacrifice of the parents, Khizr and Ghazala Khan, should be honored.
Wisconsin businessman Paul Nehlen, who is challenging Ryan in next week's primary in Wisconsin, had posted material on his campaign website accusing Ryan of misrepresenting Trump's proposed temporary ban on Muslims entering the country and defending him in the dispute with the Khans.
Several congressional Republicans have said they will not support Trump in the November 8 election against Clinton, but Hanna was the first to take the extra step of endorsing the Democrat.
Citing Trump's attacks on the Khans, Hanna called him "deeply flawed in endless ways," "unrepentant" and "self-involved."
"For me, it is not enough to simply denounce his comments: He is unfit to serve our party and cannot lead this country," Hanna wrote in a letter posted on syracuse.com, the website of the Post-Standard newspaper in New York.
Trump has had a running feud with Khizr and Ghazala Khan since they took the stage at last week's Democratic convention to cite their son's sacrifice and criticize Trump's proposed ban on Muslims.
Many Republicans have expressed support for the parents, and some have sharply rebuked Trump, most notably Senate Armed Forces Committee Chairman John McCain, a military veteran and former prisoner of war.
President Barack Obama questioned on Tuesday why Republican leaders were repeatedly criticizing Trump but still endorsing him, saying Trump's attacks on the Kahns showed he was "woefully unprepared" to serve in the White House.
"There has to come a point at which you say 'enough,'" Obama, a Democrat, told reporters.
Ryan and Republican Senate Majority Leader McConnell have offered support to the Khans, but no Republican leaders have withdrawn their support for Trump as the party's presidential pick. Ryan’s office declined to comment on Hanna’s announcement.
Hanna is retiring from the House and is not seeking re-election, leaving him more leeway to risk upsetting colleagues and voters over his break with Trump.
"While I disagree with her on many issues, I will vote for Mrs. Clinton. I will be hopeful and resolute in my belief that being a good American who loves his country is far more important than parties or winning and losing," he wrote.
Senator Ben Sasse of Nebraska, one of the most outspoken critics of Trump in Congress, said he would never join Hanna in voting for Clinton.
"Conservatives should reform the party of Lincoln, not surrender to the Clinton’s machine’s dishonesty and identity politics," Sasse said in a statement emailed to Reuters.
Trump, a former reality TV star, has troubled many in the Republican establishment with his off-the-cuff, often insulting style, and controversial policies including the proposed ban on Muslims and his plan to build a wall along the Mexican border to keep out illegal immigrants.
His presidential campaign has appealed to Capitol Hill for support amid the controversy over the Khans, including circulating talking points for lawmakers to use, but has found little support.
Trump's son, Eric Trump, told CBS News on Tuesday his father's comments toward the Khans have been "blown hugely out of proportion."
US Republican Representative Charlie Dent, who has not endorsed Trump, criticized the candidate's tone on Tuesday and called for more measured responses, telling MSNBC his "incendiary comments ... are causing real problems."
Dent added that he was not shocked by Hanna's break with the party, although he said he himself has no plans to support Clinton.
"Like me, I think he's also been very concerned about the incendiary statements plus the lack of solid policy," coming from Trump, Dent said.
Trump has fallen slightly behind Clinton in recent polls since each party held their nominating conventions last month.
He also has trailed Clinton in fundraising. The Democrat reported raising nearly $90 million in July for her campaign and the Democratic Party, with more than half the donations coming from new donors.