Donald Trump Faces Increasing Resistance From Within His Own Party

Another senator and 50 former national security officials have spoken out.

Senators Speaking Out

Collins is not the first Republican senator to say she won't be voting for Trump, but she is the highest ranking of the bunch.

Collins entered the Senate in 1997 and is now the senior senator from Maine. She served as the chairwoman of the Senate's Homeland Security Committee for four years.

"With the passage of time, I have become increasingly dismayed by his constant stream of cruel comments and his inability to admit error or apologize," Collins wrote in an op-ed for The Washington Post that was published Monday night.

She continued, "But it was his attacks directed at people who could not respond on an equal footing — either because they do not share his power or stature or because professional responsibility precluded them from engaging at such a level — that revealed Mr. Trump as unworthy of being our president."

Others Staying Away

While Collins, Sasse and Kirk have said outright that they will not be voting for Trump, there are other heavy hitters who have notably withheld their endorsement.

Trump's former presidential rival Sen. Ted Cruz has been open about his lack of support and was widely booed at the Republican National Convention when it became clear that he was not planning to endorse Trump.

"Donald Trump has left a lot of Republicans stranded, with nowhere to go in the course of this race," Dowd said.

Out of Office but Not Out of Sight

The list of former Republican officials who have returned to the public eye to denounce Trump is also growing.

Beyond that, the letter signed by 50 Republican former national security officials that was released yesterday states that none of them will be voting for Trump come November.