COLORADO SPRINGS — Flying high above the Rocky Mountains on Wednesday, Representative Paul D. Ryan and his brother Tobin jogged their memories to complete a list of the 14,000-foot summits below them that the vice-presidential nominee had climbed.

“We did that one; we did that one,” they said, consulting a list of Colorado’s famed “Fourteeners.”

It was not an idle pursuit. After Mr. Ryan walked back a claim to have run an exceptionally fast marathon, scrutiny has fallen on his other sporting pursuits, including whether he might have exaggerated his mountain climbing prowess. In this case, the brothers figured that over two decades of visits to Colorado, he had climbed above 14,000 feet “probably 38, 39 times” — potential ammunition against the doubters.

Four weeks ago, no one would have questioned such a detail of Mr. Ryan’s résumé. But since he joined the Republican ticket, every scintilla of his life, every statement he has uttered has been open to inspection. His marathon claim was debunked by Runner’s World, hardly known for political investigations.

There is perhaps no faster escalator to political superstardom in America than to be plucked as a vice-presidential candidate. Mitt Romney has spent six years in the national spotlight seeking the presidency, but for Mr. Ryan, the overnight ascension and all its trappings — speaking to millions in prime time at the Republican National Convention, a motorcade that stops traffic, imprisonment in a Secret Service bubble — has brought little time to adjust.