"April will be much more favorable to Romney," said Dick Hug, a Maryland Republican fundraiser who supports Romney.
What lies ahead in Romney path to the nomination:
WISCONSIN TILTING ROMNEY'S WAY
Romney looks strong in Wisconsin, the big prize in Tuesday's three-state mini-sweepstakes.
And he got a big boost Friday when Wisconsin's influential Rep. Paul Ryan endorsed him in a nationally broadcast television interview.
Ryan told Fox News Channel's "Fox & Friends" that he feels Romney is best suited to be the party's nominee this fall and take on President Barack Obama.
Ryan, who is chairman of the House Budget Committee, also said he's convinced that "if we drag this thing on through summer, it's going to be harder" to turn Obama out of office.
The pressure is on Rick Santorum in the former Pennsylvania senator's last chance to make the argument that he can win in the all-important industrial heartland.
Romney has had his number. He edged Santorum in Michigan and Ohio and won big in Illinois.
The formula has been simple: Swamp Santorum with TV ads and get big help from a pro-Romney group. Romney and that group, Restore Our Future, were spending about $3 million on television advertising in Wisconsin, a roughly 4-to-1 edge over Santorum and his allies.
It seems to be working. Romney has overtaken him, according to a Marquette University Law School poll published Monday.
Santorum has campaigned aggressively in conservative rural Wisconsin in the past week.
Romney has been sponsoring phone calls attacking Santorum's labor record, a hot topic where GOP activists are rallying to Gov. Scott Walker's recall election for signing anti-union legislation.
And Restore Our Future has been on television attacking Santorum since last week.
"Romney hasn't been here, but other groups are spending heavily for him," said Mary Buestin, a Republican national committeewoman from Wisconsin.
MARYLAND and DC FAVOR ROMNEY
Maryland and Washington, D.C., are a lock for Romney, despite his calling himself a Beltway outsider.
Romney has campaigned in Maryland. Santorum hasn't.
Then there's Restore Our Future again, spending nearly $900,000 on television ads for him there.
And Santorum failed to file to appear on the District of Columbia ballot.
Romney could really start to pull away Tuesday. Most of the delegates at stake in all three states are winner-take-all, not the proportional contests that dominated the first three months of voting.
Voting takes a three-week break after Tuesday. Romney will be raising money but also working behind the scenes to bring nervous conservatives into his tent.
This week he trumpeted praise from tea party icon Sen. Jim DeMint, R-S.C., and endorsements from Sen. Mike Lee of Utah, American Conservative Union President Al Cardenas and Sen. Marco Rubio of Florida.
Santorum sought to stoke doubts about Romney as a conservative by appearing outside the Supreme Court as it heard arguments about Obama's health care law.
"This is the most important issue in this election," Santorum said, referring to the 2010 law, which Romney's critics compare to one he signed in Massachusetts. "There's one candidate who's uniquely disqualified to make the case."
There's no doubt whom Santorum was talking about.
BIG EAST TOURNEY
The rest of April doesn't look much better for Santorum than Tuesday's contests.
On April 24, Connecticut and Rhode Island should be scarcely different than the string of four New England states the former New England governor has already bagged.
The same for New York, where polls have shown Romney dominating, and for Delaware, where Restore Our Future is the only group advertising.
Restore Our Future is advertising in all five April 24 primary states, including Pennsylvania.
Romney shows no signs of ceding Santorum's home state. Polls show Santorum leading, but Romney has amassed support from key GOP leaders and fundraisers.
Santorum's Senate tenure and grass-roots following give him an edge, Pennsylvania GOP strategist Leslie Gromis Baker said. But Romney is poised to outperform expectations.
"Santorum may win it, but it may not be as convincing," said Baker, an adviser to former Gov. Tom Ridge and former President George W. Bush.
MAY: SOUTH RISES AGAIN
Santorum hopes to continue to drain delegates away from Romney in North Carolina and West Virginia on May 8.
Drawing support from evangelical conservatives, he has won four of eight Southern states while Romney has won only Florida and Virginia.
Indiana's Midwestern flavor and urban pockets give Romney hope on May 8. But the race looks southward again, favoring Santorum, with May 22 primaries in Arkansas and Kentucky.
Santorum's Christian following gives him the edge in Texas, but Romney can compete. On Thursday, he added the support of former President George H.W. Bush to a long list of local and congressional GOP leaders.
Texas' huge delegate cache will be split according to the vote, and add to Romney's overall lead, even if he loses, fundraiser Hug said.
"You've got big ones in May like Texas, where, even if he doesn't win, he'll get his share of votes," Hug said.