That’s surprising. Doggett is pretty entrenched so you wouldn’t think he would make this move unless he thought it might have an impact.
Quick analysis of the potential replacements:
Harris: positives: semi-incumbent, qualified, well-known. negatives: black woman would drive opposition turnout, and she doesn’t seem to have the charisma to energize her base; not sure she’d show that well against Trump in a debate.
Whitmer: positives: Governor of a swing state, qualified, would likely show well against Trump in a debate. negatives: not that well known, female so might drive opposition turnout, blacks may not turn out for her, no incumbency
Buttigieg: positives: the most gifted/intelligent politician alive, so would destroy Trump in a debate, lots of upside with potential to win people over with his wit, extremely sharp on policy. negatives: not really qualified, and as a gay man he would be guaranteed to supercharge Trump’s base and extremely likely to turn off the black vote, only very slight incumbency
Newsom: positives: would win a debate against Trump, fairly well-known, qualified. negatives: from a deep blue state which would drive opposition turnout, no incumbency
Others: Pritzker, Beshear, Shapiro, etc.: any of these moderate Democrat leaders could step in, but they would be hard pressed to generate excitement and win swing voters in <120 days due to being relatively unknown