Fresh off the national campaign trail, Sen. Rand Paul (R-Ky.) is testing the influence of his unique political brand with a series of Congressional endorsements.

Many Kentucky political observers expect Paul to put his experience in the 2012 presidential race campaigning for his father, Rep. Ron Paul (R-Texas), to use in 2016. Some even predict the tea-party-affiliated Senator will run for president.

But for now, at least, Paul is hoping his image as a libertarian outsider can boost his preferred candidates in House and Senate primaries across the country and help reshape the GOP on Capitol Hill.

“There’s so much inertia up here, we’d like to see people come up who’d actually try to change the system,” Paul said during a recent interview in his Senate office. “I think if we don’t shake off that inertia — you know, everything is mandatory spending, everything has a permanence up here. It takes someone who is somewhat fearless and aggressive to try and change the system.”

But Paul has not limited his endorsements to outsider candidates.

The Kentucky freshman has given his blessing to Florida Senate GOP frontrunner Rep. Connie Mack IV — who is staunchly entrenched in the establishment — as well as to tea party darling Ted Cruz, who is running in Texas’ May 29 Senate primary. Paul hasn’t always picked winners, having backed losing Nebraska GOP Senate candidate Don Stenberg and New Mexico Lt. Gov. John Sanchez, who ultimately dropped out of the Senate race in the Land of Enchantment. Paul has since endorsed long-shot candidate Greg Sowards in the New Mexico primary.

But the Senator insists that all of his endorsees share certain traits, including support for a smaller government that adheres more closely to the Constitution. In today’s Kentucky GOP primaries, Paul helped recruit open 4th district candidate Thomas Massie, the tea-party-affiliated Lewis County judge-executive.

The Senator recently cut a television ad for Massie, who has been embroiled in a nasty battle against two candidates backed by the local party establishment, including the retiring incumbent. The outcome of this House primary could affect Paul’s influence going forward.

“I think people associate me with the tea party; they associate me with having great concern with the debt; having tried to be a leader in the balanced budget movement here. I think that is helpful,” Paul said. “We try to choose races where we think there’s a clear distinction between establishment moderate and what we consider to be a more constitutional conservative.”

Paul, who rocketed to national prominence after thumping the establishment-backed candidate in the 2010 primary, has hewed a careful path in his first 16 months in the Senate. Even as he votes like the libertarian upstart he campaigned as two years ago, often going against the general GOP consensus position on Capitol Hill, he has managed to earn and maintain the respect of his veteran, more establishment-minded colleagues.

These Senators have privately groused about some of the freshman tea-party-affiliated Members, who they feel have disregarded Senate decorum and tradition, assuming a combative posture while attempting to dictate ideology and strategy to the Conference. But not Paul, multiple Republicans have indicated.

One longtime K Street Republican likened Paul to former Sen. Phil Gramm (R-Texas). Gramm, this GOP insider said, talked tough and honored his principles but played well with others behind the scenes, and rather than ignoring Senate rules and traditions, he used them to advance his cause.

“He has very good personal relations with the Members of the caucus, and I think he’s learning faster than most new Senators how to maintain his principles, but work within an organization that operates by unanimous consent. Some Senators never learn that,” Sen. Lamar Alexander (R-Tenn.) told Roll Call. “Rand has views that sometime are very different than how the rest of us in the Republican caucus thinks. But he’s learned not to lecture everybody. He listens well but maintains his own principles and attitude.”

Among the more interesting developments during Paul’s short Senate tenure has been the bond he has formed with Minority Leader Mitch McConnell (R-Ky.). A productive working relationship on Kentucky issues has flourished into a personal friendship, with each Senator regularly reaching out to the other to ask for advice on politics and policy. Recently, they collaborated to prevent the closure of a nuclear power plant in Paducah, Ky., saving hundreds of jobs in the process.

Sources say McConnell has subtly communicated to others in the Senate that Paul is an ally and has his full support, even on those occasions when the tea party favorite uses the parliamentary tools at his disposal to force a vote on libertarian-minded amendments opposed by most in the chamber, regardless of party. They have come a long way since the 2010 Senate primary, when Paul defeated then-Kentucky Secretary of State Trey Grayson, who had McConnell’s strong backing.

“They have come to appreciate each other’s strengths,” said a GOP operative who monitors the Senate.

Paul, who served as a top surrogate for his father’s presidential campaign, is viewed as having a softer touch and keener political sense than the Texas Congressman.

The Senator has forged relationships with colleagues and is viewed as measured and thoughtful, defying his father’s reputation as a lone-wolf libertarian outsider. The younger Paul’s more nuanced approach to politics was on display as well on the 2012 presidential campaign trail, where he would occasionally headline events that his father could not attend.

Still, given Paul’s constitutional views and his strong conservatism on issues of debt and deficit, it’s unclear just how much establishment support he could garner if he runs for president in the future. And while his relationship with McConnell is good, he has yet to patch things up with the rest of the Kentucky GOP establishment.

Longtime Kentucky Democratic consultant Jim Cauley wondered how Paul might ingratiate himself with the national GOP establishment enough to win the nomination.

“He still bitch-slaps the Republican establishment here in Kentucky — all the time!” he said. “And I’m like, if you don’t know how to do it here, how are you going to learn to do it on a national scale?”