Harry Reid Says GOP Is to Blame for Donald Trump as Republicans Distance Themselves From Front-Runner

Meanwhile, the list of Republicans distancing themselves from Trump is growing.

The Senate minority leader blasted his Republican colleagues during a speech on the Senate floor Monday, arguing that Trump's expected nomination comes after years of work by a party that Reid says excluded groups of voters.

"He's no accident. His nomination is not some mistake. Donald Trump is the natural evolution of a party that spent eight years honing a platform that is anti-immigrant, anti-woman, anti-Obama and anti-working people," Reid said.

That said, the list of Republican leaders distancing themselves from Trump is growing.

Rubio wrote on Facebook Monday that his "previously stated reservations about [Trump's] campaign and concerns with many of his policies remain unchanged."

Senate Majority Leader Mitch McConnell took a similar path today as well, saying that Trump will likely be the Republican nominee -- and McConnell wants the nominee to win.

“I think most of my members believe he's won the nomination the old-fashioned way; he got more votes than anybody else, and we respect the voices of the Republican primary voters across the country. And we'll sit down and talk about the way forward,” McConnell said of the GOP leaders’ meeting with Trump this Thursday.

Rubio and Ayotte's statements come after a number of notable Republicans have shown they're hesitant to support their party's presumptive nominee.

James Campbell, a professor of political science at the University of Buffalo, told ABC News that enthusiasm for Trump among the party's higher-ups is tepid at best.

"After months of [Trump] trashing the party's establishment, I think this was to be expected and is understandable," Campbell said.

He added: "For Republicans, a long national nightmare still has a long way to go."

ABC News’ Alana Abramson and Ali Weinberg contributed to this report.