Almost every path to victory for President Biden relies on strong support from women. But his current standing among women is the weakest lead a Democrat has had since 2004, a key factor in how tight the race is.

Mr. Biden’s lead among women has slid to about eight percentage points since the 2020 election, according to an average of more than 30 polls conducted over the last six months and compiled by The New York Times. That’s down from a lead among women of about 13 percentage points four years ago.

And since the 2020 election, former President Donald J. Trump’s support among men has recovered and is back to the double-digit lead he had in 2016.

Republicans have generally held leads among men in most presidential elections going back decades. But every year that Democrats have won the presidency, they have led among women by more.

Mr. Biden’s drop in support has been particularly pronounced among Black and Hispanic women, according to a new set of polls focused on women across the country and in Arizona and Michigan from KFF, a nonprofit organization that focuses on health care research.