Rick Santorum enjoyed a double digit lead in some polls last week. No more. Mitt Romney has closed the gap and, according to the latest Quinnipiac poll, now trails Santorum by only 4 points:

The Republican presidential face-off in Ohio is too close to call as former Pennsylvania Sen. Rick Santorum has 35 percent of likely Republican primary voters to former Massachusetts Gov. Mitt Romney's 31 percent, according to a Quinnipiac University poll released today.

This compares to a 36 - 29 percent Santorum lead in a February 27 survey by the independent Quinnipiac (KWIN-uh-pe-ack) University poll, the day before the hotly-contested Michigan primary.

In today's survey, former House Speaker Newt Gingrich has 17 percent, with 12 percent for Texas U.S. Rep. Ron Paul. Among voters who name a candidate, 34 percent say they still might change their mind by Tuesday.

Santorum leads Romney 34 - 28 percent among men and 37 - 33 percent among women, 40 - 27 percent among self-described conservatives and 42 - 25 percent among Tea Party members. Romney leads Santorum 46 - 26 percent among self-described moderates.

"At this point, the Buckeye State is too close to call and is clearly a two-man race between Sen. Rick Santorum and Gov. Mitt Romney," said Peter A. Brown, assistant director of the Quinnipiac University Polling Institute. "A third of the electorate say they still might change their mind. With five days until Super Tuesday, they certainly will be exposed to enough negative television ads to provide fodder for those who might want to switch - or switch off."

Santorum needs Ohio more than Romney does if he wants to remain a credible candidate. Santorum is far ahead in two Super Tuesday primaries - Oklahoma and Tennessee -- and needs Ohio and probably one of the three caucuses voting on March 6 (Washington state, Idaho, North Dakota) to stay in the game. He's not even on the ballot in Virginia and Romney is far ahead himself in Massachusetts and Vermont. (Gingrich has a 15 point lead in his home state of Georgia.)

So Ohio will play a large role in next Tuesday's primaries. If Santorum wins, he will still have Romney in sight as far as the actual delegate count is concerned. If he loses, he will have to start winning some of the sweepstakes, winner take all primaries coming up in March and April to catch up.