ARLINGTON HEIGHTS, Ill. – Mitt Romney needs to win the Illinois Republican presidential primary Tuesday.

Sure, he’s way ahead in delegates to the Republican National Convention. He scored an overwhelming win Sunday in Puerto Rico’s primary, adding 20 delegates to his total.

His ads seem to be everywhere on Chicago television, and he’s got a savvy organization led by big-name local politicians.

But the former Massachusetts governor has some serious hurdles to overcome: his own persona and an electorate so sick of politics that voters may not be motivated to cast a ballot for anyone.

Romney is having trouble erasing doubts that he’s too stiff, too politically inept and too insensitive to constituents who confront gasoline prices over $4 a gallon.

He also faces voters frustrated that the economy is not improving quickly. The jobless rate in Illinois in January was 9.4 percent, down from its 11.4 percent peak two years ago but still well above the national average. And people here just witnessed the circus-like spectacle last week of an unrepentant former Gov. Rod Blagojevich heading to federal prison.

Concerned about Illinois, the Romney camp added weekend campaign stops and is spending millions on ads. They start with a built-in advantage — 54 convention delegates are at stake, but Rick Santorum only filed slates in 14 of the state’s 18 congressional districts. That means he can only vie for 44 of the delegates.

The Romney folks see a major, and perhaps even decisive, win as a plus for his candidacy, which has seen a string of victories that includes Florida, Ohio and Michigan.

But a loss would raise fresh questions about his strength.

His biggest stumbling block is Santorum, the former Pennsylvania senator, who is pushing hard for the votes of social conservatives in the Chicago suburbs and the state’s smaller communities. A poll last week found him within striking distance of Romney.

Newt Gingrich, the former House speaker, drew decent crowds during a two-day swing in the Chicago suburbs. Though polls show him with scant support, he’s planting doubts about Romney in voters’ minds.

Ron Paul, a Texas congressman, is mobilizing another constituency: He attracted an estimated 4,000 people to a rally at the University of Illinois-Champaign.

Most worrisome for Romney is that people who seem logical supporters don’t seem fired up.

They tend to be centrists, the kinds of moderate Republicans who elected a long roster of national GOP stars over the past decades — senators like Everett Dirksen and Charles Percy.

But today’s moderates often see Romney — a center-right governor of Massachusetts from 2003 to 2007 — trying to recast himself as a diehard conservative. That’s an enthusiasm-killer among centrists; early voting turnout has lagged.

“He’s the best candidate of what they have to offer, and he has a better chance against Obama,” said Doris Haack, a retired teacher from Schaumburg, a Chicago suburb. “But he needs to be more forceful, more outgoing.”

Romney and his backers hotly dispute such impressions, arguing he’s the most qualified candidate who deeply cares about his country — and has a detailed plan for action.

“I’ve actually run things,” he told a tele-town hall Wednesday. “As you know, we elected three years ago a president who’d never run anything, and it hasn’t worked out so well.” Romney’s passion problem stems from two sources. One is his style, which many find wooden and distant.

“One word: Plastic,” said Judy Thorne, a Mount Prospect, Ill., retiree.

Romney’s other dilemma involves the economy. Voters routinely quote his recent gaffes about his wife’s two Cadillacs or his friendships with NASCAR or football team owners.