Senate Minority Leader Harry Reid, D-Nev., denounced Senate Majority Leader Mitch McConnell and other GOP leaders as "cowards" for backing Republican presidential nominee Donald Trump.

"Republicans who continue to support Trump are cowards," Reid said in a Thursday statement. "They have put political party over the good of their nation. Senator McConnell is failing this critical test of leadership. He should demonstrate common decency by withdrawing his support for Trump."

McConnell has long made his dislike for Trump clear, even while insisting on party unity going into the general election. In the meantime, he's insisted publicly that Trump has to start "using a script" if he wants to be taken seriously.

With each new unscripted, controversial statement that the GOP nominee makes, however, President Obama and Democratic leaders are trying to make Republicans choose between the discomfort of backing Trump and potentially splitting the party during general election.

"Again and again, Donald Trump has proven himself unfit for the presidency," Reid said. "But instead of standing up to him, Senator McConnell has spent months enabling this unstable hatemonger."

Those attacks have come regularly in the wake of Trump's criticism of a Gold Star mother whose husband spoke at the Democratic National Convention and his apparent ignorance of the fact that Russian President Vladimir Putin has destabilized Ukraine.

"The question they have to ask themselves is: If you are repeatedly having to say in very strong terms that what he has said is unacceptable, why are you still endorsing him?" Obama told the New York Times. "What does this say about your party that this is your standard-bearer?"

Trump might have done more to undermine the case for party unity than anything Democrats could say, however, when he announced his refusal to endorse House Speaker Paul Ryan and Ariz. Sen. John McCain — who faces a competitive reelection campaign this fall — in their respective primaries.

"I like Paul, but these are horrible times for our country," Trump said Wednesday. "We need very strong leadership. We need very, very strong leadership. And I'm just not quite there yet. I'm not quite there yet."