When Donald Trump’s presidency ends in January 2021, he will be the first president in the second half of the 20th century to be forced out by his own party, prompting questions about who will take his place and who will not.

The New York Times reported that the Democrats’ challengers to Sen. Jon Tester of Montana, who has refused to support Trump’s nomination of Brett Kavanaugh to the Supreme Court, have begun privately discussing a consensus candidate who could succeed him. A senior White House official acknowledged that Republicans are considering who else could be a viable candidate for the Republican nomination, but refused to say how often they thought about it.

Among the potential candidates who have been seen as potential Republican presidential candidates are: New Jersey Gov. Chris Christie; Oklahoma Gov. Mary Fallin; Nevada Gov. Brian Sandoval; Alabama Sen. Luther Strange; Utah Sen. Mike Lee; Kansas Sen. Jerry Moran; and Wisconsin Gov. Scott Walker. None are currently familiar to national voters or endorsements.