Not to be outdone, Mr. Trump used his airborne meeting with reporters to clarify his views on immigration, saying he opposed any path to citizenship for the 11 million immigrants in the country illegally. But he did not explicitly rule out a long-term path to legal status if the nation’s immigration system is overhauled.

“We’re going to make that decision into the future,” Mr. Trump said. But, he added, “to become a citizen, you are going to have to go out and come back in through the process. You’re going to have to go out and get in line. This isn’t touchback. You have to get in line.”

On the plane, Mr. Trump also told reporters that, “as of this moment,” he planned to attend all three debates, and that only a “natural disaster” could make him change his mind. He added that, while he was preparing, he was not holding mock debate sessions.

Labor Day is traditionally the beginning of a two-month sprint to Election Day, in which candidates try to seize voters’ attention as summer fades and debates loom. Monday was no exception. The visits to Ohio by Mr. Trump and Mrs. Clinton — along with their respective running mates, Gov. Mike Pence of Indiana and Senator Tim Kaine of Virginia — highlighted the importance of a state that Republicans believe Mr. Trump must win to have any shot of reaching the White House.