Presidential historian Jon Meacham says former President Richard Nixon's Watergate scandal looks a bit like what's happening today.

Meacham, who has written biographies on Thomas Jefferson and eulogized former President George H. W. Bush earlier this month, brought some historical context to MSNBC's Morning Joe Tuesday morning. He described how Nixon's downfall coincided with an ongoing investigation and falling markets — much like what President Trump is seeing right now.

In the two-year fallout after 1972's Watergate break-in, Nixon started out claiming he was "not a crook" — something that "would've fit on Twitter," Meacham noted. From there, the economy began "souring," Meacham said, suggesting the markets could be a "barometer of what's going to happen to President Trump."

Then, Meacham brought the conversation into the present day by discussing Russian efforts to influence the 2016 election in favor of Trump. "If in fact Donald Trump knew about" these efforts, that raises the "live question" of whether these actions fit "the definition of treason in the Constitution," Meacham explained. It all makes for an "existential Constitutional crisis" in which a president could be an "agent of a foreign power," Meacham added.