This week, the Trump campaign and the R.N.C. announced a combined $55 million ad buy for the final two weeks, with the party supplementing the campaign ads in key states including Arizona, Iowa, Ohio, Michigan, North Carolina, Florida, Pennsylvania, Georgia, Nevada and Wisconsin.
The R.N.C. entered October with $78.1 million cash on hand, after it had spent $36 million more than it raised in September in its effort to lift Mr. Trump in the final months of the election.
Other Republican megadonors have donated large sums to super PACs to help Mr. Trump, none more so than Sheldon Adelson, the casino magnate, who along with his wife, Miriam, contributed $75 million to a pro-Trump advertising effort.
Timothy Mellon, the banking fortune heir, donated $10 million to a different pro-Trump super PAC, along with $21 million from Isaac Perlmutter, the chairman of Marvel Entertainment, and his wife, Laura Perlmutter.
Also on Tuesday, a Silicon Valley-linked super PAC supporting Mr. Biden, Future Forward PAC, announced $66 million in donations since July, with nearly half of the money coming from dark money groups that do not disclose their donors. The biggest named donor was Dustin Moskovitz, a Facebook co-founder, who gave nearly $22 million. Eric Schmidt, the former chief executive of Google, also contributed $2.5 million to the group in total this year.
Michael Crowley contributed reporting.
