Last year, Rep. Paul Ryan (R-Wisc.) was hailed as the man with a plan to save America. Today, barely half of his own party thinks highly of him.

According to a Rasmussen poll released Monday, Ryan's approval rating has plummeted since the November election. In the poll, only 35 percent of likely voters said they had a favorable view of him, while a 54 percent majority said they viewed him unfavorably. That's a stunning reversal from last August, when 50 percent of voters liked Ryan, versus 32 percent who did not.

While the poll found that Republicans still generally supported their party's budget guru, even they've rapidly soured on him in the past few months. A slim 52 percent of Republicans now view him favorably, a far cry from the 83 percent who said the same back in August.

So what happened to Ryan's once-shining star?

For one, the Romney-Ryan ticket suffered a convincing November defeat, prompting the party to conduct a deep soul-searching mission and to propose a major rebranding effort. Yet as the party prepares to move forward, Ryan has held back.

In his new budget outline unveiled last week, Ryan once again put forward the policies he championed in the 2012 election: Lower tax rates across the board and cuts to programs aimed at the poor. Those policies did not sit well with voters last year, and they're not getting any more popular. Even the Republican National Committee conceded that point, saying the GOP had to change its ways because voters considered the party's positions "scary" and "out of touch."

As for Ryan's decline among Republicans, he could be suffering from a conservative desire for fresh faces and ideas, which was evident at last week's Conservative Political Action Conference. Ryan delivered the keynote address, but other speakers, notably Sen. Rand Paul of Kentucky and Sen. Marco Rubio of Florida, garnered far more attention.

"Ryan risks falling into the Jack Kemp trap: Doomed to be 'a thought leader' in the House like the man he once worked for, who was also a losing GOP vice presidential nominee," Politico's James Hohmann warned in his post-CPAC review.

Though the event's straw poll is a largely meaningless predictor of a presidential primary, it does to some degree gauge the support for potential candidates among the party's more conservative wing. Ryan placed a distant fifth in that poll, behind Paul, Rubio, New Jersey Governor Chris Christie, and even former Sen. Rick Santorum (Penn.).

Part of the reason for that may have been Ryan's failure to offer a compelling vision for the party's future.

From the National Journal's Rebecca Kaplan:

"At CPAC, Ryan was not selling a GOP vision for future elections. He was selling the GOP vision for the fiscal fights underway right now: Curb spending, cut the deficit, and scale back the scope of government. He ceded any 2016 political positioning to Rubio and Sen. Rand Paul, R-Ky., who gave back-to-back speeches outlining their different visions for the country." [National Journal]

Ryan's fall from grace could be exacerbated by a revolt from the right. His new budget proposal, though generally considered extremely conservative, has been criticized by fellow Republicans for counting billions in tax increases from the fiscal cliff deal, as Businessweek's Joshua Green notes. Rep. Paul Broun (Ga.), a member of the House Tea Party Caucus, said as much in a New York Times op-ed, writing that Ryan's budget "fails to seriously address runaway government spending."

Given his role as House Budget Committee chairman, Ryan remains a highly influential figure in the GOP. But as the party begins to rebrand and search for a new standard-bearer, Ryan risks becoming a marginalized figure — an ideas guy with no buzz.