Democrats can only install a new candidate if Biden withdraws his candidacy. Already high level discussions are starting, and in the House, Jamie Raskin, (D Maryland) is the one to watch. I figured he'd be in the top five of either talkin' Biden out of running or pulling the trigger on the 25th amendment. They just need to stomach the will to put it out there. A simple replacement is not only illegal, but it dis-enfranchises every Democrat voter who went in for Biden in the primaries. I wonder if the Democrat Party and the Deep State would risk doing that when they are so desperate to not only install but keep in power the Progressive Socialist movement to achieve their "One Party Rule". Quite a few 'Crats in Congress don't support the progressive idiocies, but then when it comes time to vote, they hold the party line in the sake of unity in such closely aligned quarters as both Houses. 1 or 2 votes in the Senate against Schumer and the party, or just a handful in the House going along with the right would be a disaster as far the Democrats are concerned. The wailing and gnashing of teeth from them and the media would be astounding.
As of today, they're screaming about the SCOTUS (6-3 decision) in favor of some limited immunity for the President. Already calling for 4 more justices in the SC, mainly because they believe the SC is the next highest authority in the enactment of law; just an extension of Congress and the President, therefore they want to hold the majority in the SC. With that passed, and the 'Crats holding the Senate, you'd probably see 4 new Democrat Justices with a couple of weeks.
Since there should be absolutely no party bias in the SC when deciding a case, as only the Constitution should be the deciding factor, I would like each of the 9 justices to issue a one page opinion of why the legislation or law supported the Constitution, or why they felt that it was un-constitutional, and make it public. I believe you'd immediately see who tows the party line and who don't.