Rep. Mark Sanford said the political honeymoon is over for President Trump, noting the "weird stuff" he's done while in office had eroded respect for him inside the Beltway.

GOP lawmakers are becoming more comfortable challenging their party's standard-bearer, Sanford told NPR when asked about the House and Senate's overwhelming support of ratcheting up sanctions on Russia and limiting Trump's power to change them.

"Very few people would walk very far out on the plank in opposing a new, incoming president," the South Carolina Republican said during an interview that aired Monday.

"He's done some weird stuff. It's been noted. It's impacted, I think, some of his level of respect with regard to the country at large or certain members of the political process in Washington."

But Sanford, who has co-signed a bill that would require future presidents-elect to release their tax returns, said some Republicans were hesitant to back the measure out of fear of "a bad tweet" from the president.

Trump refused to disclose his returns during the 2016 presidential campaign because he claimed they were still under audit. An Internal Revenue Service audit would not preclude someone from releasing their tax returns on their own.

"I mean, I don't want that. Nobody's looking for a bad day," Sanford said. "The president can be quite vigorous in his pronouncements. And you don't want to be at the receiving end of one of those."

However, in this case, Sanford said that preserving "a 50-year tradition" was of "greater importance."