See How Biden Lost Support in the Polls Before He Dropped Out

President Biden ended his re-election campaign on Sunday after a post-debate slump in national and swing-state polls. In less than four weeks, his position had deteriorated in three Rust Belt states crucial to his re-election, as former President Donald J. Trump’s once narrow polling leads grew wider.

Mr. Biden fell again in the polls after a gunman’s attempted assassination of Mr. Trump at a Pennsylvania rally on July 13. The president lost support in Michigan, Pennsylvania and Wisconsin, as well as other swing states where he had already been trailing by four to five points.

Mr. Biden’s path to the presidency narrowed as his standing in the swing-state polls dropped, most likely a factor in his decision to drop out of the race. Multiple Democratic officials publicly shared their concerns about recent polling trends in urging him to step aside.

Polls and the Electoral College

Might the polls have been wrong, or have underestimated support for Mr. Biden? It’s possible, but his deficit was nearing the edges of the biggest polling misses in recent elections. Assuming the polls did not change before Election Day, he would have needed the polling margins in Wisconsin, Pennsylvania and Michigan to miss by at least five points in his favor.

The Times has published an update to its polling averages that shows Mr. Trump with a narrow national lead over Vice President Kamala Harris, who is now the most likely Democratic nominee. Most of the polls were conducted before she was a candidate, and there are currently few or no polls of the new matchup at the state level. It may take at least a week or two to gain a broader understanding of how Ms. Harris’s entry will affect the race.