CHICAGO (CBS) — The number two Democrat in the U.S. Senate stood up for a Republican colleague who has found himself in President Donald Trump’s crosshairs amid a war of words over the president’s leadership ability.

Calling Corker a natural leader and respected colleague, U.S. Sen. Dick Durbin called Trump’s criticism of Corker a mistake, and said it will make more Republicans question whether the president will support them.

“As the president attacks his own Republican party, and the leaders in that party, I’m sure more and more Republicans wonder if this president will stand by them when they really need him,” he said.

Last month, Corker announced he wouldn’t run for re-election, and on Sunday, Trump blasted Corker in a series of tweets, claiming the senator “begged” for an endorsement, and dropped out when Trump refused.

Corker has flatly disputed asking for an endorsement, saying Trump urged him to run again and promised to endorse him if he did. In a New York Times interview, Corker also accused the president of treating his office like “a reality show,” and of putting the U.S. “on the path to World War III” with his threats toward North Korea and other nations.

Corker also traded barbs with Trump on Twitter, posting that “the White House has become an adult day care center” under Trump.

Durbin said he texted U.S. Sen. Bob Corker after reading about Trump lashing out against the retiring Tennessee Republican on Twitter.

“I thanked him for his candor, and his honesty, and his courage, and I told him that he’s going to play a critical role and have a strong voice for the next year and a half as he serves the United States Senate,” Durbin said.