I think that The Atlantic tracks your IP and gives you a certain number of free reads, after which you'll need to start a trial or subscribe.
Serwer raises some interesting points. However, I still think that Biden should declare that he's not running for reelection rather than resign if he wishes to pull out of the presidential race. For example, Biden could state that he's resigning to spend more time with his family.
As Vice President, Harris could argue that she has ample qualifying experience for the office of President; actually serving as President up until the election is, I think, unimportant.
Moreover, if Harris were the Democratic nominee for President with Biden retaining the office until Jan 6th, she would likely have more time to campaign than if she were both nominee, and President - with its attendant duties and obligations.
Finally, the 25th Amendment states:
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.
The Republican-controlled House would block any nominee for Vice President, and take full advantage of the vacancy to attack Harris and create political mayhem.