Kentucky Sen. Rand Paul is back on the national political stage, endorsing Indiana Rep. Marlin Stutzman in his primary fight for the state’s open Senate seat.

The primary between Stutzman and fellow Rep. Todd Young is a high-profile contest between the conservative and establishment wings of the Republican party.

“We cannot continue to elect politicians who will support the status quo,” Sen. Paul said in a statement. Calling Stutzman a “principled conservative,” Paul added, “[w]e need leaders who will fight to dismantle the power structure in Washington and return our government to the people.”

Rand’s fellow Kentucky Senator, Senate Majority Leader Mitch McConnell, has put his resources on the other side of the Indiana primary fight. Two PACs tied to McConnell, the Senate Leadership Fund and One Nation, are pouring $1 million into the race to back Rep. Young.

The primary battle between Stutzman and Young was triggered by the retirement of Sen. Dan Coats, who returned to the Senate in 2010 after a previous retirement. Both Stutzman and Young were elected to the House in the Republican wave of 2010.

They both entered Congress as strong conservatives, but have taken very different paths in Washington. Young is backed by the US Chamber of Commerce, in addition to McConnell, and is characterizing Stutzman as an ineffective ideologue.

“We have too many D.C. politicians — too many poseurs and pretenders who will talk a good game, but do not have any results in the end to show for it,” Young said criticizing Stutzman.

Stutzman told the AP that Young’s idea of success is “passing a bill out of the House that goes nowhere in the Senate.” He added, “[t]he American people are starting to figure out that things are not getting any better for us and they are tired of it.”

Club for Growth, Freedomworks and Senate Conservatives Fund are backing Stutzman in the primary. Stutzman is also a member of the House Freedom Caucus. The Chamber of Commerce has endorsed Young and is planning to spend $1 million backing his campaign.

The primary almost ended before it began. Rep. Young was short the necessary number of signatures to get on the ballot. The state’s Election Board deadlocked on whether Young should be thrown off the ballot, and that allowed his campaign to continue. A majority vote by the Board was necessary to rule his candidacy ineligible.

Republicans members of the Election Board argued that Young’s failure to meet the signature threshold was simply an oversight.

The May 3 primary is occurring against the backdrop of a pivotal GOP Presidential primary where frontrunner Donald Trump, Sen. Ted Cruz and Gov. John Kasich are battling for the state’s 57 winner-take-most delegates.

Stutzman’s campaign message against the Washington Republican establishment should resonate with supporters of both Trump and Cruz. In primaries to date, though, the Presidential race has had very little impact on down-ballot races.

In many ways, though, the Indiana Senate primary is a fight that predates the current Presidential primary and will continue long after 2016 is in the history books. It continues the ongoing and very real battle for the future of the Republican party.

Sen. Rand Paul’s entry into the race shows he has reengaged in that debate. It is a debate that will linger long into the night.