As Mr. Ryan completed his first week as the Republican vice-presidential candidate, whooshed overnight to the highest level of American celebrity with its perks and poison darts, he might have wished once or twice that he was in Colorado, climbing another Fourteener, which is how he had planned to spend the week if Mr. Romney did not call.

State troopers now block interstate highway traffic to allow his motorcade to pass. At the same time, on Friday TMZ posted a picture of him shirtless, and he has experienced a head-spinning level of scrutiny from every detail of his record in office to whether his suit coats are cut too big.

He stumbled a little under the intense exposure, denying he had requested funds from the federal stimulus while denouncing it in 2009 as a “wasteful spending spree.” That was Wednesday. By Thursday, he said that he had taken a closer look at his records and acknowledged requesting money on behalf of conservation groups from his Wisconsin district.

Over all, Mr. Ryan easily passed the “deer in the headlights” test that undermined the rollout of an earlier Republican vice-presidential pick, Dan Quayle, in 1988.

He has drawn crowds in the thousands in Colorado, Nevada, Ohio and Virginia, who applauded throughout his 20-minute stump speech even at lines that offer only medium-rare meat.

He has had at least two years of tempering as a Republican lightning rod for his aggressive House budgets. And he says he has led more than 500 town hall meetings about Medicare, a topic already heating up the summer.

With that in mind, Mr. Ryan has been prepping for his two biggest challenges before Election Day: an October debate with Vice President Joseph R. Biden, Jr., whose expertise in foreign affairs should put Mr. Ryan on the spot, and his acceptance speech at the party convention in less than two weeks.

In advance of the debate, Mr. Ryan has had policy briefings with Dan Senor, a senior adviser to Mr. Romney who is an expert on Israel and the Middle East, and also crafts speeches. On Tuesday, Mr. Senor boarded the candidate’s plane in Denver with two fat briefing books under his arm. They later were open on a table at the front of the plane as Mr. Ryan pored over them on the flight to Las Vegas.

His front-of-the-plane entourage also includes two venerable Republican speechwriters working on his convention address, John McConnell, who worked for President George W. Bush, and Matthew Scully, who wrote the Sarah Palin speech four years ago that electrified the party.

But unlike Ms. Palin, Mr. Ryan has no need to introduce himself to the party base, which knows and loves him already.

While vice-presidential candidates are usually given the job of attack dog, letting the candidate at the top of the ticket strike a statesmanlike tone, this has not been Mr. Ryan’s job, as widely expected. The roles were reversed this week, with Mr. Romney charging that Mr. Obama “disgraced the presidency” and telling him to take his “campaign of division and anger and hate back to Chicago.”

Mr. Ryan, for now, has been the portrait of amiability on the stump.