Republican strategist Alex Castellanos warned President Trump Sunday to shore up his legal team because he could face a "storm" of trouble from special counsel Robert Mueller's Russia probe, which could be exacerbated if the GOP loses its stranglehold on power in Congress after the 2018 midterms.

"It's hard to believe that somebody like Donald Trump, who has flaunted his weight in business success, that Robert Mueller is not going to dig up something in Trump's complicated financial history to say, 'Look, the president of the U.S. did this and it was wrong,'" Castellanos told ABC's "This Week."

"And it's hard to believe then when Republicans lose the House in 2018, maybe by 40 or 50 seats, that the House is not going to impeach him. And it's also hard to believe the 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 continued.

Castellanos concluded, "Get good legal help now because a storm is coming," speaking directly to Trump.

In March, John Dowd, one of Trump's top personal lawyers, resigned after publicly calling for the removal of Mueller.

The news was followed by reports the president has had difficulties filling out his legal team.

Castellanos consulted on the political campaigns of Bob Dole, President George W. Bush, Jeb Bush, and Mitt Romney.