Illinois Republicans head to the polls today to choose their presidential nominee.

Chicago Tribune: “For a state that is home to President Barack Obama and run by Democrats, the grueling, months-long GOP battle for the nomination provides the state’s out-of-power Republicans with a real say on national politics for the first time in decades. Democratic voters, meanwhile, will decide several heated congressional contests in newly drawn districts.”

“At stake are not only Illinois’ 54 elected national convention delegates, but for Mitt Romney, the chance to gain much-needed momentum with a big-state victory. For a vastly outspent and out-organized Rick Santorum, a win in Illinois would upend Romney’s slow drive to the nomination and fuel questions about the former Massachusetts governor’s electability and ability to unify core GOP conservatives.”

Smart Politics: “Only one Illinois Republican presidential primary has been decided by less than 10 points out of 25 contests since 1912.”

Polls close at 8 pm ET.

Rick Santorum explains to Real Clear Religion why he’s losing the Catholic vote despite being Catholic himself.

Said Santorum: “I’ve heard different excuses and different explanations from different people. I think one of the reasons is that Catholics are certainly not a monolith. They don’t vote like a minority anymore; in other words, they don’t vote in a bloc. And I think that’s a good thing, actually… I think that shows that Catholics have, by and large, assimilated into the religious milieu of this country. I think that’s probably the biggest part of it. In fact, I don’t know how many Catholics actually know I am a Catholic.”

GQ reveals the Secret Service code names chosen by the top two Republican presidential candidates: Mitt Romney elected to call himself “Javelin.” And Rick Santorum chose “Petrus.”

“It’s tempting to associate a candidate’s code word with some aspect of their personality. Sometimes this is true and sometimes it is not. ‘Petrus’ is a biblical allusion — as in St. Peter, the first pope. (The Latin name is derived from the Greek word for ‘rock.’) Perhaps ‘Javelin’ is a reference to the ’60s muscle car made by American Motors Corporation, the company once run by George Romney.”

“I don’t care what the unemployment rate’s going to be. Doesn’t matter
to me. My campaign doesn’t hinge on unemployment rates and growth rates.
It’s something more foundational that’s going on.”

— Rick Santorum, quoted by National Journal.

In a surprise announcement, the Arizona Daily Star reports Ron Barber (D), the long time district director for former Rep. Gabrielle Giffords (D-AZ), said he would run for office in Arizona’s newly-drawn 2nd congressional district later this year.

Barber is already running to complete his former boss’ term in the 8th congressional district special election to be held on June 12. He is a survivor of the January 8, 2011 shooting in Tucson which also injured Giffords.

Rick Santorum’s campaign offered ABC News “a sneak peek at their in-house delegate tally, which still shows the former Pennsylvania senator trailing Romney but in a much better position to catch him.”

Here’s how the Santorum campaign sees the standings in the race for delegates: Romney 435, Santorum 311, Gingrich 158, Paul 91

Here is the ABC News delegate estimate: Romney 521, Santorum 253, Gingrich 136, Paul 50

“Their delegate equation largely rests on two key assumptions: First, that Arizona and Florida will eventually allocate their delegates proportionally rather than using their current winner-take-all scheme. Second, that delegate tallies in Iowa, Missouri and Washington State should be estimated based upon the preliminary results of ongoing county and district conventions, not on the initial ‘beauty contest’ votes.”

Roll Call lists the top ten most vulnerable House members up for re-election this year — six Republicans and four Democrats.

“He’s not overwhelming, that’s the problem through the whole damn
primary. What’s the spark? What’s the thing that gets him off and
running? No one knows.”

— Former House GOP leader Bob Michel (R-IL), quoted by Politico, on Mitt Romney.

“This is all about getting delegates. If the polls are right, we’ll pick up some delegates. That’s what it’s all about.”

— Mitt Romney, quoted by ABC News ahead of the Alabama and Mississippi primaries last week.

“I know a lot of people will talk about delegates and strategies and math and that’s all very interesting to the insiders. But I think the American people want to see someone who has the leadership, skill and experience to defeat the president, and a vision of conservatism that will get American back on track again.”

— Romney, in an interview yesterday on Fox News Sunday.

A new Global Strategies Group poll in Indiana finds Sen. Dick Lugar (R-IN) leads his GOP primary rival Richard Mourdock (R) by just six points, 45% to 39%.

In what First Read calls “another gut punch” for Mitt Romney, former Mississippi Gov. Haley Barbour (R) told ABC News that he voted for Newt Gingrich last week in his state’s GOP primary.

Said Barbour: “I didn’t endorse anybody. I didn’t want to try to influence anybody’s vote, so beforehand I didn’t say who I voted for. But Newt and I have been friends a long, long time… Out of friendship, I voted for Newt.”

A new Washington Post-ABC News poll finds two-thirds of Americans say the U.S. Supreme Court should throw out either the “individual mandate” in the federal health care law or the law in its entirety — signaling the depth of public disagreement with that controversial element of health care reform.

The Supreme Court opens hearings on the law’s constitutionality next week.

Meanwhile, BuzzFeed notes President Obama’s re-election campaign “has launched an all-out defense of his landmark, and unpopular, health care overhaul, a move that marks a realization: The issue can’t be avoided.”

“This is someone who doesn’t have a core. He’s been on both sides of almost every single issue in the past 10 years.”

— Rick Santorum, on CBS’s This Morning, about Mitt Romney.