Something to remember here, is that no sitting US president; who has faced a serious primary challenge, has won reelection since Lyndon B. Johnson (D-Texas) in 1964. Historically, even modest primary challenges; like Pat Buchanan’s stab at George H. W. Bush (R-Texas) in 1992, can be fatal to an incumbent president.
Daniel G. Jennings
So we might not need Joe Biden after all. The GOP could do themselves in without any assistance from the Democrats. Or, to put it another way, Trump has just sold the GOP a 3-mile spool of rope.