While the Republican-run Senate is almost certain to vote for keeping President Donald Trump in office, that hasn’t stopped his critics from talking about the potential for a “President Pence” or a “President Pelosi.”

So as Trump’s impeachment trial proceeds, here’s a look at how the presidential line of succession is currently set in U.S. law.

If Trump is ousted or resigns, Vice President Mike Pence would take the reins and presumably quickly pick a fellow Republican to serve as his vice president, just as Gerald Ford succeeded Richard Nixon and tapped Nelson Rockefeller as his No. 2.

But if Pence, a former Indiana governor, is somehow not available, the line of succession gets into the weeds a little.

Next in line is House Speaker Nancy Pelosi, the California Democrat, followed by the Senate’s most senior Republican, Sen. Chuck Grassley of Iowa, known as that chamber’s president pro tempore.

After that, members of Trump’s Cabinet are tapped, starting with the secretary of state (currently Mike Pompeo), followed by the Treasury secretary (Steven Mnuchin), defense secretary (Mark Esper), the attorney general (Bill Barr) and the interior secretary (David Bernhardt).

The line of succession then goes on down through the rest of the Cabinet, with the order based on how long ago their department was created, so the head of the Department of Homeland Security, founded in 2002, is last. Chad Wolf heads that department in an acting capacity as he has not been confirmed by the Senate. A further wrinkle is that Trump’s transportation secretary, Elaine Chao, isn’t eligible to ascent to the presidency because she is not a natural-born U.S. citizen, having been born in Taiwan to Chinese parents. (She is married to Senate Majority Leader Mitch McConnell.)

Don’t miss: Complete MarketWatch coverage of the Trump impeachment inquiry

Trump, charged with abuse of power and obstructing Congress, is only the third American president to have been impeached by the House of Representatives, joining Andrew Johnson and Bill Clinton. Nixon resigned before an impeachment vote could take place.

Impeachment by the House, of course, doesn’t mean removal from office. Neither Johnson nor Clinton was found guilty in their impeachment trials in the Senate, and the same outcome is widely expected in the impeachment of Trump, whose Republican Party occupies 53 of the chamber’s 100 seats. That helps explain why the stock market DJIA, -0.35% SPX, -0.21% hasn’t reacted much to impeachment-related developments. A two-thirds majority of senators is required to vote to convict Trump to remove him from office.

Opinion: For the stock market, impeachment is just a sideshow

And read: Why investors are so calm about impeachment — and what it would take for that to change

Democratic lawmakers’ push to remove the president from office centers on Trump’s pressure on Ukrainian President Volodymyr Zelensky to announce investigations into Democratic presidential candidate Joe Biden and his son, as well as into a theory that Ukraine interfered in the 2016 presidential election.

Trump has frequently criticized Democrats’ efforts, saying in a December letter to Pelosi that “more due process was afforded to those accused in the Salem Witch Trials.”