SPRINGFIELD, Ill. (AP) — Illinois voters were set to nominate potential successors Tuesday for ex-U.S. Rep. Aaron Schock, once a rising Republican star who resigned amid questions about his use of taxpayer and campaign funds for worldwide travels and the "Downton Abbey"-styled redecoration of his congressional office.

The race in the Republican-leaning district was shaping up to be a classic GOP primary battle between the son of a former congressman and U.S. transportation secretary against a conservative writer with strong tea party support.

State Sen. Darin LaHood has been treated like the incumbent with high name recognition, early state GOP backing, hefty fundraising and key endorsements, including from the National Rifle Association. But Michael Flynn, who helped start a news website with late blogger Andrew Breitbart, has said no candidate should be hand-picked for Congress and has railed against establishment Republicans.

During the truncated campaign season, Flynn has tried to play up Ray LaHood's work in President Barack Obama's first administration, while the younger LaHood has said he's "much more conservative" than his father.

Republican Donald Rients, who works for State Farm, is also running, along with two candidates in the Democratic race: Springfield school board member Adam Lopez and high school teacher Robert Mellon.

The key in the expansive district that touches 19 different counties will be turnout, which is expected to be light. The special primary — with just one race on the ballot in a nonpresidential election year — comes in peak summer vacation season. By comparison, turnout in the February 2013 special primary to replace Democratic former U.S. Rep. Jesse Jackson Jr. hovered around 10 percent in the Chicago area district, with a far larger media market for campaign ads and more geographically compact.

"When it's a low turnout, crazy things can happen," said Matthew Streb, a political science professor at Northern Illinois University.

Light turnout typically benefits the party-backed candidate with loyal voters motivated to cast ballots, but that's not always the case. There's the reminder of last year's stunning upset in Virginia — when Dave Brat, a tea-party backed economics professor, defeated then-U.S. House Majority Leader Eric Cantor in a Republican primary.

All candidates have tried to differentiate themselves from Schock during candidate forums, home visits and on social media, saying the district needs a fresh face.

Tea party activists say the support for Flynn has been grass-roots, while Republican party officials believe it'll be tough to beat LaHood because of his experience and familiarity to voters.

The special general election is Sept. 10.

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Tareen reported from Chicago.

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