A conservative rock star in the marbled halls of Congress, Paul Ryan — his ideas, his politics, his very name — was just barely beginning to register at the Spot Cafe off State Road 16 here Sunday.

Rick Paul, said one diner, was a brilliant vice presidential choice. Mike Ryan, said another, would surely boost Mitt Romney’s presidential campaign and help “save the country.” At last, said Jim Smith, 74, Romney made a decision that solidifies his conservative credentials.

“Paul — from Kentucky?” Smith said, referring to the junior Kentucky senator, Rand Paul. “Definitely a good move. I didn’t support Romney in the primary, but I will now with Paul in there.”

And so it went Sunday in the crucial swing state of Florida, in the GOP stronghold of St. John’s County, and just down the bright gray highway from where the presumptive Republican presidential nominee is scheduled to campaign Monday without his vice presidential pick, the man named Paul Ryan, 42, a congressman from Wisconsin.

A rising player among conservatives in Washington, Ryan was only vaguely familiar to the breakfast crowd at the Spot Cafe, where diners were mostly older than 50, representing a critical demographic Romney needs to win Florida.

“I know nothing about that gentleman,” said Stuart Joseph, 79, heaping sugar into his coffee.

And about Ryan’s plan to cut the federal budget?

“Nothing,” Joseph said, stirring.

About Ryan’s plan to restructure Medicare?

“Nope,” Joseph said, sipping.

Ryan’s relative obscurity here stands in contrast to the large crowds that greeted him and Romney at campaign stops this weekend in Virginia and North Carolina, and to pundits already speculating about whether Ryan will motivate Romney’s conservative base or spook baby boomers and seniors across Florida with his Medicare plan.

“Paul Ryan’s his name?” asked Floyd Register, 62, a county worker who hasn’t quite decided who he will vote for in November.

And so, TV and radio advertising in Florida for the next three months is likely to be relentless: President Obama’s campaign will cast Ryan’s proposal as the death knell of Medicare, and Romney will cast it as the program’s only salvation.

For Romney, the process launched Sunday, when he and Ryan, whose mother is on Medicare in Florida, appeared on CBS’s “60 Minutes” and introduced Ryan’s proposal as one that will save Medicare for future generations.

“You’re going to have to do a little selling,” reporter Bob ­Schieffer said to Romney, a point that diners underlined Sunday.

Told in general terms that Ryan’s plan would restructure Medicare for future generations of seniors, Register said that he would need to know more details before deciding whether it would affect his vote.

“It’s the unknowns” that concern him, he said.

At another table, Lorina Johnston, 54, said she heard the name Paul Ryan for the first time Saturday, and immediately went online to find out more about him, looking at Fox News, MSNBC, ABC and other Web sites.

Although she is leaning toward Romney, Johnston, who is being treated for breast cancer, said that Ryan’s Medicare proposal “does make you a little nervous.”

Asked whether the prospect of changing Medicare could sway her from voting for Romney, she said, “It could.”

A recent survey conducted by The Washington Post and the Kaiser Family Foundation found that 58 percent of Americans want Medicare left alone, but there is no fresh polling data on how that question plays in Florida.

For the most part, the breakfast crowd at the Spot seemed to be a Romney crowd, and even those who had never heard of Ryan imagined he could do little to dissuade them from voting Republican, even changing Medicare.

Once he understood that the vice presidential candidate was Paul Ryan and not Rand Paul, and that Ryan had a proposal to change Medicare, Jim Smith shrugged it off.

“I’m so negative on Obama,” Smith said, explaining that he would vote for Romney no matter what.

There were a few Sunday who knew exactly who Paul Ryan was, and who were glad to see that Romney had chosen him as his vice presidential running mate. They were eating eggs and French toast at table near the window, debating whether Ryan’s Medicare proposal, which they supported, was a winning campaign theme.

“It has to be sold. . . . Romney needs to get the word out about it and not run from it,” said Leny Pearson, 41, who works in marketing. “We can’t just keep on avoiding it.”

His dining companion, David Larry, was not so sure that the country was ready for that complex discussion.

“That won’t get him elected,” said Larry, 80, a retired engineer. “Getting him elected is the key. We can be policy wonks later.”

A few tables over, Gene Johnson, 73, and his friend Doug, 70, who did not want to give his last name, agreed that Romney’s campaign will have a tough time selling Medicare reform in Florida.

But they say that addressing the country’s fiscal issues is critical. And they have faith that Romney’s vice presidential pick is up to the task of explaining his Medicare proposal to voters.

“The thing about Romney is, he’s on the up and up,” Doug said. “Whether it’s popular or not, he and Mike Ryan are out to save the country.”

“Yep, I think Rand’ll do all right,” said Johnson, referring to the Kentucky senator.