You don't know that anymore than anybody else unless you have a crystal ball. You're simply conveying your own bias.
I can go by historical odds. Presidents usually get re-elected. Since 1900, 15 incumbent presidents have been re-elected - McKinley, T. Roosevelt*, Wilson, Coolidge*, FD Roosevelt (3 times), Truman*, Eisenhower, LBJ*, Nixon, Reagan, Clinton, Bush-43, Obama
(*- I am counting guys who took the job because the main guy died in office).
The only time they don't is if
1) They really, really fucked it up. (Hoover, Trump, Ford)
2) They angered a part of their coalition who defected to a third party (Bush-41, Carter, Taft)
Even not particularly good/popular presidents get re-elected, such as Bush-43, or Nixon, or Harry Truman. Heck, even Jerry Ford came damned close to a second term, despite pardoning Nixon, losing Vietnam and wrecking the economy, and he never got elected on a national ticket to start with. That's how much you get from incumbency.
It all depends on who the Republicans run against him. A lot of people are going to be reluctant to reelect an 82 year old man to the presidency knowing the more than fair odds he won't live to finish the term.
A president hasn't died in office from natural causes in 76 years. People know that these guys get the best medical care in the world. And frankly, I'd like to be as vigorous as Biden is at 79.
As long as the Republican candidate isn't Trump Part II they will have that advantage right out of the gate.
Will they? The Republicans haven't won the popular vote since 1988 except for one time, and they had to scare the hell out of us to do it.
The problem with the GOP is that they have to pander to a base that is basically nuts. They can't walk that back after the election. And frankly, what incentive do they have to not be Trump II, Electric Bugaloo? Trump excites the base. Even if Trump doesn't run, they'll have to outcrazy each other to get the same result.
I doubt very much Biden runs again anyway, so the point is likely moot.
Well, you guys can hope. Biden or not, Republicans still have the same problem. It's become a white identity party in a country that is increasingly anti-racist.