Democratic presidential candidate Pete Buttigieg's sexuality has become a campaign issue after a radio host questioned if voters would pick a man "kissing his husband on stage".
Firebrand conservative Rush Limbaugh said Democrats must realise America is still not ready to elect a gay man.
Mr Buttigieg's Democratic rivals leapt to his defence, and President Donald Trump said he would vote for a gay man.
Mr Limbaugh was last week awarded a top civilian honour by the president.
On his radio show which is nationally syndicated to millions of listeners, Mr Limbaugh on Wednesday imagined Demcorats' deliberations over who to vote for.
He said: "They're saying, 'OK, how's this going to look? Thirty-seven-year-old gay guy kissing his husband on stage, next to Mr Man, Donald Trump.'"
If elected, 38-year-old Mr Buttigieg would be the first openly gay US president. He is the former mayor of South Bend, Indiana, a city of just over 100,000 people.
Mr Buttigieg did not directly address the radio host's remarks during an event in Las Vegas, Nevada, on Thursday night, but said: "I'm proud of my marriage. I'm proud of my husband."
His campaign declined to comment.
The real question is who wants to kiss Rush Limbaughhttps://t.co/MoA3shCYFM— Victory Fund (@VictoryFund) February 12, 2020
President Trump was asked in an interview with a Fox News journalist on Thursday if he would be open to voting for a gay candidate.
"I think so," the Republican president said. "I think there would be some that wouldn't, and I wouldn't be among that group, to be honest with you.
"I think that it doesn't seem to be hurting Pete Buttigieg."
According to Pew Research, the proportion of Americans in favour of same-sex marriage is at 61%, a number that has levelled out in the last few years after steadily rising for a decade.
Former Vice-President Joe Biden, who has been beaten by Mr Buttigieg in the first two votes of the presidential primary season, in Iowa and New Hampshire, lashed out at Mr Limbaugh.
He said on ABC's daytime chat show The View on Thursday: "It is part of the depravity of this administration… Pete and I are competitors, but this guy has honour, he has courage, he's smart as hell."
But conservative commentators defended Mr Limbaugh.
The Federalist magazine said the radio host's remarks were not homophobic.
"Operatives in Buttigieg's own campaign have asked these questions in deciding how he should approach being the first openly gay major presidential candidate," said its article.
Influential Republican Senator Lindsey Graham of South Carolina said: "I think the country is not going to disqualify somebody because of their sexual orientation."
But he rejected any suggestion that the Presidential Medal of Freedom, which First Lady Melania Trump last week bestowed on Mr Limbaugh, should be withdrawn.
"Well, my God. Free speech still exists," he said.
Ben Ferguson, a conservative radio host, said he has spoken to Democratic voters on his show who are unsure if Mr Buttigieg's sexual orientation could hamper him in defeating Mr Trump.
"There was a surprising number of Democratic voters who said it was an issue for them," he told CNN. "The reality is what Limbaugh was talking about."
In Iowa's caucuses last week one voter asked to rescind her ballot for Mr Buttigieg after learning he was gay.
"I don't want anybody like that in the White House," she said. "So, can I have my card back?"