Kansas Gov. Sam Brownback today endorsed Republican presidential candidate Marco Rubio, calling the Florida senator "a true conservative." Brownback's endorsement makes for the first sitting governor to endorse a 2016 Republican candidate, reported the Guardian.

Rubio's campaign made the announcement in a statement that lauded Brownback as "one of the most conservative governors in the country" who has been "one of the nation's strongest defenders of the unborn, limited government, and traditional values," reported the Hill.

Brownback's endorsement of Rubio as a "true conservative" is most damaging to Ted Cruz, who has sought to dominate that role in the field and is, perhaps, more closely aligned with Brownback than Rubio on most policy issues. Brownback also noted that it was a matter of pragmatism, saying Rubio would be best positioned to defeat either of the Democratic candidates in the general election.

"Marco Rubio is a true conservative who can unite the party and defeat Hillary Clinton or Bernie Sanders in the fall," said Brownback. "In the past, conservatives have been forced to make a choice between their heads and their hearts. This year, we are fortunate to not have to make that choice." Brownback added that Rubio "has a proven track record of protecting life, defending religious liberty and undoing Obamacare."

Kansas will hold its caucuses March 5, just after "Super Tuesday" votes in which 13 states will hold primaries or caucuses.

The endorsement comes just ahead of the South Carolina primary where, according to recent polling, Rubio is in third place behind Donald Trump and Ted Cruz. In recent polling averages compiled by RealClear Politics, Trump has 37 percent support, followed by Cruz with 17 percent and Rubio trails with 14.3 percent support. On a national scale, Rubio remains in third place, but by a closer margin. Trump leads with 29 percent, Cruz is in second with 21 percent and Rubio in third with 20.3 percent.