Legally, even a conviction would not prevent Trump from running for President. Legal experts have already affirmed that fact.
This is all about the Suburban Woman vote. The Donks want Trump stained as a serial adulterer, which is why the Stormy Daniels name matters. If they can force Trump to be in a New York courtroom in January and February, that hurts his ability to campaign, and experts have already said that even a conviction would see 12 months to 18 months in the appeals process, guaranteeing the matter could be kept hot and fresh all through the election.
Males will vote for Trump if he gets the nomination. But more women than men vote, and Democrats want Republicans, not just Trump, stained as the morally creepy party, just ignore Joe and Bill Clinton and all those guys.
The 'best case' for Democrats is for Trump to lead the GOP race most of the primary season, but not win the nomination. That way, Dems hope to have an angry Trump split the GOP vote and guarantee whatever idiot or corpse the Democrats run will win.
There are a lot of ways that plan could blow up in the Democrats' face, but that's for a different thread.