Front-runner Mitt Romney won the Illinois primary with ease Tuesday night, routing Rick Santorum in yet another industrial state showdown and padding his already-formidable delegate lead in the race for the Republican presidential nomination.
Romney triumphed after benefitting from a crushing advantage in the television advertising wars, and as his chief rival struggled to overcome self-imposed political wounds in the marathon race to pick an opponent to Democratic President Barack Obama.
Preliminary exit poll results showed Romney preferred by primary goers who said the economy was the top issue in the campaign, and overwhelmingly favored by those who said an ability to defeat Obama was the quality they most wanted in a nominee.
The primary capped a week in which the two campaigns seemed to be moving in opposition directions - Romney increasingly focused on the general election battle against Obama while Santorum struggled to escape self-created controversies.
Most recently, he backpedaled after saying on Monday that the economy wasn't the main issue of the campaign. "Occasionally you say some things where you wish you had a do-over," he said later.
Over the weekend, he was humbled in the Puerto Rico primary after saying that to qualify for statehood the island commonwealth should adopt English as an official language.
While pre-primary polls taken several days ago in Illinois suggested a close race, Romney and Restore Our future, a super Pac that backs him, unleashed a barrage of campaign ads to erode Santorum's standing. One ad accused the former Pennsylvania senator of changing his principles while serving in Congress, while two others criticized him for voting to raise the debt limit, raise his own pay as a lawmaker and side with former Sen. Hillary Rodham Clinton to support legislation allowing felons the right to vote.
In all, Romney and Restore Our Future outspent Santorum and a super PAC that backs him by $3.5 million to $500,000, an advantage of 7-1.
Neither Newt Gingrich nor Ron Paul campaigned extensively in Illinois.
Romney and Santorum did, though, and not always in respectful tones.
"Senator Santorum has the same economic lightweight background the president has," Romney said at one point. "We're not going to replace an economic lightweight with another economic lightweight."
Santorum had a tart reply. "If Mitt Romney's an economic heavyweight, we're in trouble."
Including Romney's victory last weekend in Puerto Rico, the former Massachusetts governor had 522 delegates going into the Illinois voting, according to The Associated Press count. Santorum had 253, Gingrich 135 and Paul 50. If Romney continues on the same pace, he will lock up the nomination before the convention opens in Tampa, Fla., next August.
However, the Santorum campaign argued Tuesday that the race for delegates is closer than that.
Santorum contends the Republican National Committee at the convention will force Florida and Arizona to allocate their delegates on a proportional basis instead of winner-take-all as the state GOP decided. Romney won both states.
Illinois was the 28th state to hold a primary or caucus in the selection of delegates to the nominating convention, about halfway through the calendar of a Republican campaign that has remained competitive longer than most.
A change in party rules to reduce the number of winner-take-all primaries has accounted for the duration of the race. But so has Romney's difficulty in securing the support of the most conservative of the GOP political base. Santorum and Gingrich have struggled to emerge as the front-runner's sole challenger from the right.
Whatever the reasons, the race appeared unlikely to end soon, with Santorum and even Gingrich vowing to campaign into the convention.
Next up is a primary Saturday in Louisiana where Santorum projects confidence following twin triumphs a week ago in Alabama and Mississippi. There are 25 delegates at stake.
Behind Louisiana is a three-primary night in the District of Columbia, Maryland and Wisconsin on April 3, with 95 delegates combined at stake.
Santorum is not on the ballot in Washington, D.C., but is ahead in opinion polls in Maryland. Wisconsin - adjacent to Illinois - shapes up as the most competitive primary of the night.