Held at arm’s length by many Republican leaders, Mr. Trump also has few high-profile surrogates to help him deliver his closing message. He has relied mainly on members of his family, including his wife, Melania, who campaigned in the crucial Philadelphia suburbs on Thursday in her first public speech since the Republican convention in July.

Mrs. Clinton has flexed her organizational power on the ground and on the air: Seizing on what Democrats believe is a spike in Hispanic turnout in some states, she has adjusted her television advertising, nearly doubling her spending in conservative-leaning Arizona, another heavy early-voting state, in an attempt to snatch it away from Mr. Trump.

And in North Carolina, Mrs. Clinton’s campaign has focused heavily on college communities and areas with a high concentration of black voters. Mrs. Clinton rallied black voters near Greenville on Thursday afternoon, before an appearance alongside Senator Bernie Sanders of Vermont in the Raleigh area. Her campaign has paid for ads in student newspapers and on vans that can take students to the polls, and has swarmed campuses with volunteers.

The Clinton campaign has also begun making supporters pick up tickets for large-scale rallies and concerts in person, rather than taking R.S.V.P.s online. The reason: It can draw them close to early voting centers and then nudge them to cast their ballots.

Should Mrs. Clinton run up a sufficient lead over Mr. Trump in early voting, it could become impossible for him to win North Carolina. Mrs. Clinton or another high-profile surrogate has stumped in the state every day this week, before the last day of early voting on Saturday. Bill Clinton was there on Sunday; Senator Tim Kaine of Virginia, her running mate, on Monday; Vice President Joseph R. Biden Jr. on Tuesday; and Mr. Obama on Wednesday, and he was due back on Friday.

Outside Greenville on Thursday, Mrs. Clinton assailed Mr. Trump as a threat to black America: She branded him as a practitioner of racial discrimination who “thinks the lives of black people are all crime and poverty and despair.”