A Republican strategist on Sunday warned President Donald Trump to build up his dwindling legal team because a “storm is coming” in the form of special counsel Robert Mueller’s Russia investigation.

Alex Castellanos, who has worked on campaigns for Jeb Bush and Mitt Romney, told ABC’s “This Week” it’s hard to believe that “Robert Mueller is not going to dig up something in Trump’s complicated financial history to say, ‘Look, the president of the United States did this and it was wrong.’”

He went on to say a switch in Republicans’ fortune in Congress after November’s midterm elections could bring dire consequences for the Trump presidency.

“And it’s hard to believe then that when Republicans lose the House in 2018, maybe by 40 or 50 seats, that the House is not going to impeach him,” Castellanos said.

“And it’s also hard to believe that a U.S. Senate that’s going to be scared to death, though may still be in Republican hands, is not going to take a serious look when it has to deal with this president,” he said. “So get good legal help now, because the storm is coming.”

Trump’s legal team, according to numerous reports, has been reduced to two or three attorneys after John Dowd, his lead lawyer, resigned on March 22 after quarreling with the president over how to respond to Mueller’s prosecutors.

Dowd urged a more cooperative approach and advised Trump not to agree to a sit-down interview with Mueller.

But Trump favored more aggressive tactics and spoke about his desire to be grilled by Mueller.

In the days around Dowd’s departure, a number of high-profile lawyers, including former President George W. Bush’s solicitor general, decided against joining the team.

Trump is now mainly represented by Ty Cobb and Jay Sekulow, who have been advising the president in Mueller’s probe since last summer.

This report originally appeared on NYPost.com.