Sen. John McCain (R-Ariz.) was reminded Friday of the disadvantages of being an incumbent this cycle.

After spending the week at the heart of the legislative debate surrounding the repeal of the Pentagon's "Don't ask, don't tell" policy, McCain was scheduled to fly back to Arizona on a 6 a.m. flight.

He's facing a tough primary challenge from former Rep. J.D. Hayworth (R-Ariz.) and had a series of campaign appearances lined up Friday, starting with a town hall event in the Phoenix area.

But McCain's flight had mechanical problems and was delayed leaving Washington. His campaign subsequently had only a few hours' notice to reschedule to Saturday the town hall event in Fountain Hills.

This wasn't the first time McCain missed a campaign appearance because his responsibilities kept him in Washington.

On May 14, McCain failed to make the opening of his Tucson campaign office because his flight was grounded by weather during a layover in Dallas. His campaign staff were left scrambling to find a replacement for the senator and eventually had to settle for Tucson Mayor Bob Walkup and local car dealer Jim Click.

"He flies commercial; this happens to everyone," said McCain spokesman Brian Rogers.

That's certainly true. But in a year when incumbents need to campaign hard to save their jobs, the challenge of getting back home from D.C. is an added complication.

And it doesn't look like the Senate's summer schedule will provide any respite.

On the docket: the financial regulatory reform conference report, Elena Kagan's Supreme Court confirmation, the war supplemental conference report, an extension of jobless benefits, a defense authorization, small-business loans and other jobs bills, plus a budget resolution.

It seems McCain's campaign staff can expect more delays.

— Walter Alarkon contributed to this report.