By Special Contributor Larry Kane

PHILADELPHIA (CBS) – In campaign 2012, Rick Santorum fights on, but he’s not far from the biggest showdown.

The next few days are critical for the survival of the Rick Santorum campaign. Tuesday was a real chance for Santorum in Wisconsin but Romney has overtaken him in the polls there, although it could be close.

Then there is Pennsylvania on April 24th. Pennsylvania was supposed to be a slam dunk for Santorum but the latest polls show Romney closing fast. The big question is – if Santorum loses Wisconsin, Maryland and D.C. on Tuesday, how long will he carry on and risk being embarrassed in his home base.

The pressure is on unless he wants to go the Gingrich route and hope for a nasty floor fight at the Tampa convention in August. One small clue, Santorum is saying that he would take a Vice President slot but the intensity of his attacks might prevent that from ever happening.