(CNN) – The status of Rick Santorum's presidential bid is "irrelevant" following Tuesday's elections, Mitt Romney backer Sen. John McCain said on Wednesday.
The 2008 Republican presidential nominee said Romney must now pivot to the general election and focus on restoring his image, bruised by the GOP primary fight.
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"Whether Rick Santorum stays in or not, is now basically irrelevant and Mitt has a lot of ground to make up," McCain said on CNN's "Starting Point with Soledad O'Brien." "I'm confident he can make it up, but every day that goes by that he's not in the general campaign is a day lost."
The senior Arizona senator said Romney's unfavorable ratings are high due to the bitterest primary battle he has observed. McCain said Romney, the former Massachusetts governor, pivoted affectively toward President Barack Obama Tuesday night following victories in Wisconsin, Maryland and Washington, D.C., something he must continue to do given Santorum's bleak delegate outlook.
Santorum vowed once again on Tuesday night to remain in the nomination fight, despite a trailing delegate count and falling national and state wide poll numbers. Romney currently has 648 delegates, well ahead of Santorum's 264, according to a CNN estimate. Romney must win 44% of the remaining delegates to reach 1,144 delegates necessary to clinch the nomination. Santorum needs to win 79% of the remaining delegates to do the same.
Assuming Romney becomes the nominee, McCain urged him "not to rush to judgment" when picking his running mate. He predicted a difficult decision for Romney given the potential picks, who he said included Sen. Marco Rubio of Florida, New Jersey Gov. Chris Christie, Indiana Gov. Mitch Daniels and Louisiana Gov. Bobby Jindal.
McCain specifically touted the virtues of nominating Rubio for the No. 2 spot.
"I think obviously Marco Rubio would be one of the prime contenders for a whole variety of reasons, including by the way he's been a very impressive senator during the time he's been in the Senate," McCain said of the freshman tea party favorite.