It was just a few months ago that Republican Sens. Rand Paul and Marco Rubio brought the Conservative Political Action Conference crowd to its feet with back-to-back speeches that left many in the audience waxing poetic about the two freshman firebrands and their prospects in 2016.

But while Paul earned similar praise Wednesday from activists perched on the Capitol lawn for a rally against illegal immigration and the IRS, the very mention of Rubio's name drew groans and even boos. The same Tea Party types that helped catapult Rubio into the national spotlight have now turned on him as he continues to maneuver the Senate toward a bipartisan, comprehensive immigration reform package.

"He's making a decision based on his personal ambition and not what's best for the country," said Debbie Agliano, whose husband, William, noted they were once fans and have a Rubio sign in their Hanover County, Va., garage.

"I still like him," William Agliano adds. "But he's making it tough."

There are few in the crowd as conflicted about Paul, who came to the stage to a rowdy applause from the hundreds protesting the IRS for targeting conservative groups. Paul drew laughs immediately by claiming he stole Senate Majority Leader Harry Reid's phone and brought it to the rally.

"You think the NSA is going to be surprised when they see Harry Reid at a Tea Party?" Paul joked.

"I think we can have freedom, security, the Constitution and the Bill of Rights," Paul added, striking a more serious tone. "I'm horrified that my government has gotten out of control and is persecuting people for their political and religious beliefs, and it needs to end now."

It was all taken in by the frustrated activists, who earlier in the day heard from radio show host Glenn Beck and the anti-immigration reform wing of the Republican party, Reps. Louie Gohmert, of Texas, and Steve King, of Iowa. From drones to the IRS scandal to immigration, Paul's outspokenness continue to excite the GOP base.

When asked why he liked Paul, Richard Nowell of Pennsylvania put it plainly: "He's right, he's right, he's right. On every issue, he's right."

Paul and Rubio were elected as part of the conservative wave that swept the 2010 elections, and began both instantly became two of the Republican Party's rising stars. When Rubio was picked to deliver the Republican response to President Obama's State of the Union address this year, Paul followed him, speaking on behalf of the Tea Party.

At the March CPAC confab in Maryland, Rubio drew rave reviews for insisting Republicans should not back down from their platform after the disheartening 2012 election.

"We don't need a new idea," Rubio said then. "There is an idea. It's called America. And it still works."

Rubio has since emerged as the GOP point man on immigration reform, juggling the concerns of the conservatives who elected him and the need to hammer out a proposal that can pass both the House and Senate.

On Wednesday, while Paul and another speaker, Sen. Ted Cruz of Texas, were received with chants urging them to run for president in 2016, the mere mention of Rubio, who wasn't even there, elicited jeers from the crowd.

But while the immigration battle has hurt Rubio among the GOP faithful, some conservatives say they're willing to forgive.

"I'm still hopeful," said Nowell's son, Justin, a Baltimore city school teacher. "I hope he played with fire once and he had enough."

steve contorno Congressional Correspondent