The president praised Portman as "honorable" last week for corroborating his explanation of why Ukraine aid got held up. The second-term senator said Trump had explained to him it was because he believed European allies needed to do more, not because he needed Ukraine to probe Biden as a condition to receive the money. Portman was among the senators in both parties pressing Trump to release the aid to Ukraine to help counter Russian influence in the region.

Trump's calls for foreign probes into Biden are the centerpiece of House Democrats' impeachment efforts. Portman urged the House to be “very careful” before moving forward on impeachment and lamented that his style of bipartisan legislating will take a hit.

Portman joins Sens. Susan Collins (R-Maine), Mitt Romney (R-Utah) and Ben Sasse (R-Neb.) in expressing concern for the president’s calls for China to probe Biden. A number of other Republicans have insisted the president wasn’t serious when he made those comments last Friday.

“I doubt if the China comment was serious to tell you the truth,” Sen. Roy Blunt (R-Mo.) said on “Face the Nation” Sunday. “I don't know what the president was thinking. But I do know he loves to bait the press and he does that almost every day to see what you'll talk about.”