In the endorsement, Rubio cited Cotton's time serving in the Army's 101st Airborne before saying that the Arkansas congressman would fight hard to repeal Obamacare if elected to the Senate.
"He won't stand down when it comes to repealing ObamaCare, fighting to lower our runaway debt, and turning back the tide of big government that has taken over Washington in recent years," Rubio said in the email. "Make no mistake: helping Tom Cotton secure a victory in Arkansas is vital to conservatives nationwide who wish to reclaim America from the liberals that have taken our country in the wrong direction. Doing so requires winning the majority in the U.S. Senate.
"The liberals won't give up easy. Tom's opponent is one of Barack Obama's most reliable votes, which means Washington Democrats will be pumping millions into this race."
Cotton, considered a rising GOP star, can now add Rubio to a list of endorsements from prominent Republicans and conservative groups backing his campaign for Sen. Mark Pryor's (D-AR) Senate seat. Cotton has already been endorsed by the Club for Growth and the American Crossroads group. The Senate Conservatives Fund has also aired ads attacking Pryor early after Cotton jumped into the race.
Earlier on Tuesday the National Republican Senatorial Committee released an ad attacking Pryor. The ad argued that Pryor only pretends to be a moderate and is secretly a liberal who eagerly supports major initiatives of President Barack Obama, like Obamacare, even though Pryor was more conservative than all but two Senate Democrats in 2012.
Notably, the endorsement did not mention immigration reform. Cotton has expressed strong opposition to the bipartisan immigration reform proposal Rubio supported in the Senate. Pryor was one of the 60 senators who voted for the immigration reform bill.