Tens of millions of dollars in campaign ads have cluttered the city’s stoops and televisions. Candidates sparred face-to-face in two televised debates. And the last of the big-name endorsements have trickled in.

Now, with just days left, the critical Democratic primary for mayor of New York City has shifted into an urgent final footrace to push every last supporter in the five boroughs to the polls.

The round-the-clock effort took on fresh urgency this weekend, as the weather forecast for Primary Day on Tuesday threatened to bring dangerously high temperatures that some campaigns fear could keep older voters at home.

The nearly dozen Democratic candidates planned to fan out across the city on Saturday, but most eyes were on the two front-runners, former Gov. Andrew M. Cuomo and Assemblyman Zohran Mamdani, and the vastly different approaches they were taking to try to tip the outcome.

Mr. Cuomo, a 67-year-old moderate, is reprising an old, and conspicuously expensive, playbook he has used in statewide races. While his super PAC pounds Mr. Mamdani with millions of dollars in negative commercials and mail, he appears to be largely relying on labor unions and paid canvassers to carry his message to subway stops and doorways.

“I have 650,000 women and men in organized labor,” Mr. Cuomo boasted on Tuesday after rallying with hundreds of carpenters, electricians and metal workers in Manhattan’s Union Square. “Does he?”