Austin Petersen is trying to pull off a difficult task: doubling the number of libertarian-leaning Republicans in the U.S. Senate.

Sen. Rand Paul, R-Ky., was re-elected just last year with 57.3 percent of the vote in a mostly quiet election cycle for Republicans inspired by his father's two GOP presidential campaigns. He is so far the only one to make it into the upper chamber.

"Libertarians have a messaging problem, not an ideas problem," said Petersen, 36. Ambitious and energetic, he is running for Senate in Missouri, a state President Trump carried by nearly 19 points in November, hoping to win the Republican nomination to challenge incumbent Democratic Sen. Claire McCaskill.

Maine state Sen. Eric Brakey, 29, is running on a similar platform to become the Republican challenger to Sen. Angus King, an independent who caucuses with the Democrats. "He's much less of a Bernie Sanders independent and much more of a Hillary Clinton corporatist type who hands out favors to big-government cronies," Brakey said of his would-be opponent.

"Angus King has been around in politics in the state for as long as I've been alive," said Brakey. "There's a big opportunity here in the state of Maine for us to pick up this U.S. Senate seat."

Both Petersen and Brakey plan to run to the right of the Democrats on fiscal issues while expanding the Republican coalition by hitting their opponents on criminal justice reform and corporate welfare.

"Conservatism runs deep in both parties here," said Petersen. "Even the Democrats in Missouri are very strongly traditional on issues like abortion and gun rights." Yet he believes he could do better appealing to African-American voters in places like St. Louis County, where criminal justice issues boiled over in Ferguson, than more conventional Republicans. Sen. Roy Blunt, R-Mo., squeaked through to another term by three points last year even as Trump was winning the state handily.

"I see this in my own state senate races," said Brakey. "A constitutionalist, libertarian message can appeal to the very strong conservative base of the Republican Party while also appealing to independents and even socially liberal voters."

Rep. Raul Labrador, R-Idaho, is the most established figure who is popular with the libertarian wing of the party who will try his hand at a statewide race next year. Labrador, a Freedom Caucus member, announced in May that he is running for governor. "Idaho needs a proven conservative leader who will stand against the special interests and politicians that have picked the winners and losers in our state Capitol for too long," he said in a statement.

Former Texas Rep. Ron Paul served 12 terms in the House as a Republican, most of them in obscurity, before becoming a national political figure with his 2008 presidential bid. He ran a second time in 2012, nearly doubling his raw primary vote total to more than 2 million and finishing in the top three in both Iowa and New Hampshire.

That was good enough to get other like-minded candidates to run as Republicans on platforms that included opposing the Iraq war, ending the Federal Reserve and making deep cuts to federal spending. Paul's son Rand was first elected to the Senate in the Tea Party wave of 2010. Rep. Justin Amash, R-Mich., won his House seat that same year. Rep. Thomas Massie, R-Ky., joined them in 2012.

Since those quick early victories, the momentum has stalled. The elder Paul retired from Congress. His son was believed to have a legitimate chance of capturing the Republican presidential nomination in 2016, but saw Sen. Ted Cruz, R-Texas, and even the populist upstart Trump steal some of his base. The younger Paul dropped out after a disappointing finish in Iowa, a state where his father's supporters briefly captured the party leadership and won him a majority of the unbound delegates four years earlier.

Petersen has picked an easy general election target in McCaskill, who is widely considered to be one of the most vulnerable Democrats up for re-election in 2018. "You could beat her just by calling her Obama's senator or Hillary's senator," said Jeff Roe, a Missouri-based Republican strategist. When one pollster tested several potential GOP candidates against McCaskill, Roe said, "Everyone beat her."

But you can't make it to the general without winning the primary first, which will be no easy feat. Republican insiders consider Missouri Attorney General Josh Hawley, who opened an exploratory committee earlier this month, the overwhelming favorite. The national party and conservative outside groups are prepared to devote considerable resources to supporting Hawley.

If anyone is able to put a roadblock in the way of Hawley's nomination, Republicans familiar with the race expect it will be Missouri Treasurer Eric Schmitt, who garnered national interest himself. Petersen may not even have the libertarian wing all to himself as state Rep. Paul Curtman, a 2012 Ron Paul endorser, launched an exploratory committee in July.

Petersen sought the Libertarian Party presidential nomination last year, winning praise for his strong stand against abortion from conservatives seeking an alternative to Trump. The eventual nominee, Gary Johnson, and his running mate, William Weld, both former Republican governors, supported abortion rights.

King is at present heavily favored for re-election in Maine. There has been persistent speculation about whether Gov. Paul LePage will enter the race on the Republican side.

"The Rand Pauls of the world, when they come along, great," said Cliff Maloney, president of Young Americans for Liberty. "But we need to start building a bench at the local level."

The focus on national races has obscured some libertarian Republican successes in local contests, Maloney said, such as the mayor's offices in Aberdeen, Md., and Ocean Springs, Mississippi. "There's a big difference in perception between running as local schmuck versus local mayor," he added. "It's really about having credibility."

"Everyone starts as a guy in the community," said Brakey. "But it's a lot easier to run for mayor, or run for state senator and try to prove yourself before you run for Congress. People take you a lot more seriously."

The libertarian message for government may apply to politics too. "It's better," he said, "to start small."