The National Rifle Association endorsed conservative commentator Christine O'Donnell Friday in Delaware's Republican Senate primary. The Tea Party-backed O'Donnell is looking to upset Rep. Mike Castle (R-Del.) on Tuesday.

The NRA's Political Victory Fund cited O'Donnell's "commitment to preserving the Second Amendment" in its endorsement of her Friday.

“Christine O’Donnell will be a strong voice in fighting ongoing efforts by anti-gun politicians to dismantle the Second Amendment,” chairman of the NRA's Political Victory Fund Chris Cox said in a statement. “We ask all Delaware gun-owners and hunters to vote for Christine O’Donnell in the U.S. Senate Republican primary on September 14th.”

The NRA's endorsement made no mention of Castle, but the longtime congressman earns an "F" from the gun lobby for his voting record. 

The NRA backing comes as Castle and O'Donnell are in a battle of last-minute "conservative" endorsements, which is at least one metric where O'Donnell seems to have come out on top over the past two days. 

Former Alaska Gov. Sarah Palin officially backed O'Donnell Thursday, while Castle's campaign touted in-state endorsements from former Delaware Gov. Pete du Pont (R) and former Judge Bill Lee, who ran for governor in 2008.