There is some speculation floating around social media (mostly, but not totally, from the right) that Democrats may try to pull the 25th Amendment card on Biden to push him aside and bring Kamala Harris forward in an effort to save face in this moment of geopolitical crisis. It is some of the same speculation you saw several times when the Left called for members of the Trump administration to turn on Trump and invoke the amendment.
However, the Democrats have put themselves into such a terrible position that they absolutely cannot get rid of Biden through this means, or else they give up the only chance they have to get anything through the Senate, and they would definitely hurt their electoral chances in 2022 and 2024.
In August of 1974, Gerald Ford became the President of the United States after Richard Nixon resigned. In order to get a Vice President, Congress had to approve Nelson Rockefeller.
“Whenever there is a vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take office upon confirmation by a majority vote of both Houses of Congress,” Section 2 of the amendment explains.
This last happened in 1974, when Vice President Gerald Ford — himself a replacement for Vice President Spiro T. Agnew, who resigned after being accused of tax evasion — replaced President Richard Nixon. Ford nominated Nelson Rockefeller to serve as his vice president, according to the Gerald R. Ford Presidential Library and Museum.
Via the 25th Amendment itself:
In case of the removal of the President from office or of his death or resignation, the Vice President shall become President.
Whenever there is a vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take office upon confirmation by a majority vote of both Houses of Congress.
This is a problem for the Democrats. Kamala Harris is currently the tie-breaking vote in the Senate, and Republicans are only crossing over if Mitch McConnell supports a bill or if he realizes the Republicans will lose the fight anyway. He has a very tight grip on his caucus, and he can get his 50 votes whipped if he wants to make a stand. So far, he hasn't had to. But there is a lot of power to be had in a 50-50 Senate with no tie-breaking vote, and he will take advantage of it.
So, Kamala Harris becoming the President via the 25th Amendment means the Democrats lose their tie-breaking vote in the Senate, and without a 51st vote, there is no way for the Democrats to break a tie in the Senate in order to confirm a replacement Vice President. They are effectively stuck.
But the question is also whether or not the Democrats even want Harris to be in charge. Her polling is absolutely dreadful. There are a lot of whispers in the background about her being unable to even run a political office. The Biden team doesn't seem happy with her, Democratic leadership is staying silent about her, and the media is not even trying to cover her out of fear it would make her look worse (and, given her track record, it absolutely would).
She is probably the one person Democrats are less enthused about right now than Biden. And, between Biden, Harris, Nancy Pelosi, and Chuck Schumer, there doesn't seem to be a sound leader among the Democrats in D.C. right now, and it's pretty well exposed to the rest of the country at this point. That makes any public confidence in the party virtually zero right now, and if they somehow manage to scrape by in 2022, it will be with even tighter margins than we see now — and that's without trying to remove Biden from power via the 25th Amendment. Can you imagine how badly the public trust in the Democrats will tank if they are forced to remove their “moderate, sensible” president from office?