WASHINGTON — The sexual assault accusation against Judge Brett M. Kavanaugh hasn’t just upended what was expected to be his relatively easy Senate confirmation to the Supreme Court. The allegation has also scrambled the political calculations for 10 Democratic senators running for re-election in states won by President Trump, particularly three moderate Democrats who had been weighing a yes vote.

Few politicians have a greater stake in Judge Kavanaugh’s fate than these 10 senators who are trying to appeal to red-state voters back home, and whose re-election bids will determine whether Democrats win control of the narrowly divided chamber in November.

Before Christine Blasey Ford accused Judge Kavanaugh of assaulting her when they were teenagers, many of these senators were simply happy that the Kavanaugh nomination hadn’t become a rallying cry for the conservative base. They hoped they could vote no without political consequences, because he was so likely to be confirmed with Republican votes, and then move on to more favorable terrain.

And for three of the most moderate Senate Democrats — Heidi Heitkamp of North Dakota, Joe Manchin III of West Virginia and Joe Donnelly of Indiana — the nomination represented an opportunity for them to vote yes on Judge Kavanaugh and demonstrate independence from their party and deny Republicans an issue in the fall campaign. The three had previously supported President Trump’s first nominee for the court, Justice Neil M. Gorsuch.