Last week, senior Trump campaign officials huddled with the Republican National Committee leadership in Washington, D.C., to hash out spending plans for the race’s final days, a discussion that included the possibility of taking out a loan or delaying payment on some bills past Election Day to fully fund operations, according to a person familiar with the matter.

Perhaps nothing underscores how acute and unexpected the budget situation is for Mr. Trump as much as his television ad budget. His cash on hand entering October was $40 million less than the $104.4 million he had previously reserved in television ads for the final five weeks, according to Advertising Analytics data. So earlier this week, Mr. Trump’s campaign and the R.N.C. announced that the party would begin funding coordinated ads in many key states, a move that lessens the financial squeeze on Mr. Trump.

Over all, the data show Mr. Trump’s TV ad spending has shrunk by $23 million since Sept. 20. In that same time period, Mr. Biden has expanded his reservations by $99 million.