Nearly two dozen current, former GOP lawmakers have now come out against Trump

Sen. Susan Collins
Evan Vucci | AP

Donald Trump's presidential campaign has long had a rocky relationship with the rest of the Republican Party.

But in recent days, a growing number of current and former members of Congress have joined their fellow Republicans in opposing him.

At least 22 current or former Republican members of Congress have now voiced opposition to his candidacy, in some cases even endorsing Democrat Hillary Clinton.

Maine Sen. Susan Collins, in a Washington Post op-ed this week, wrote that "I will not be voting for Donald Trump for president. This is not a decision I make lightly, for I am a lifelong Republican." She cited Trump's comments about the Muslim parents of a fallen U.S. soldier and his questioning of the impartiality of a judge based on his Mexican heritage as among her reasons for denying her support.

Collins has some company within her party in the Senate when it comes to opposing Trump. South Carolina Sen. Lindsey Graham, Illinois Sen. Mark Kirk, and Nebraska Sen. Ben Sasse have said they will not support Trump's campaign. Kirk went so far as to rescind his previous endorsement and air an ad against Trump.

In the House, Rep. Richard Hanna of New York has said he will vote for Clinton, writing that "[Trump] is unfit to serve our party and cannot lead this country." In a first for the current Congress, Rep. Scott Rigell of Virginia has said he will vote for Libertarian Gary Johnson for president.

That is not to say Trump does not have support from the Republican Party's leadership in many respects. House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell have endorsed thew New York tycoon. But the number of defections within party ranks has raised eyebrows, and accelerated in recent days as Clinton has pressed to recruit Republicans and independents.

Here is a list of current and former congressional Republicans who have voiced opposition to Trump or are supporting another candidate, as compiled by CNBC: