Aamer Madhani

USA TODAY

DECATUR, Ill. — Sen. Mark Kirk, perhaps the most vulnerable Republican lawmaker facing re-election, finds himself mired in the toughest battle of his legislative career as he tries to fend off a strong challenge from Democratic Rep. Tammy Duckworth in a race complicated by the presence of Donald Trump at the top of the GOP ticket.

Kirk insists he remains virtually deadlocked with Duckworth and confidently assures supporters on the campaign trail that he is positioned to win re-election.

But the contours of the contest — one of nine competitive Senate races that are expected to decide which party will control the Senate in the next Congress — tell a different story.

In his race against Duckworth, a two-term congresswoman and Iraq War veteran, Kirk has trailed in a trio of nonpartisan polls of the race, and the Rothenberg & Gonzales Political Report has rated the contest as leaning Democratic.

Kirk was the first federal GOP lawmaker to rescind his endorsement of Trump, when in June he announced he could no longer support the Republican nominee after he questioned whether a federal judge could be impartial, because of his Mexican heritage.

Still, Duckworth and her surrogates have repeatedly branded Kirk as a Trump lackey. President Obama told supporters at a fundraiser for Duckworth and Illinois Democrats this month that Kirk was incapable of being a “check on somebody like the guy running for President at the top of the Republican ticket.”

For his part, Trump on the stump has assessed that Kirk’s campaign is “not doing so well” while dismissively noting “that’s his problem.”

Making matters worse for Kirk, who suffered a stroke in 2012 that has left him using a wheelchair, he has lost the backing of the Republican-leaning editorial board of the Chicago Tribune.

The paper, which had endorsed his six previous successful runs for the House and Senate, cited concerns about Kirk’s abilities to carry out his duties in its decision to endorse Duckworth, who lost two legs while fighting in Iraq.

“All of my races for office it’s been predicted I would be defeated — including my five races for Congress,” Kirk said in an interview aboard his bus following a campaign stop in this Central Illinois city. “We’ve always won by (running) way ahead of top of the Republican ticket.”

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Indeed, Kirk — who has touted himself as a moderate in a blue state by voting with Democrats for stricter gun laws, supporting same-sex marriage and rejecting his party’s effort to defund Planned Parenthood — has had success in attracting ticket-splitters.

He ran 11 percentage points ahead of George W. Bush in 2004. He ran more than 17 percentage points ahead of the GOP presidential nominee John McCain in a successful 2008 re-election to his former congressional district north of Chicago.

And in his 2010 race for Senate, Kirk tallied 41,200 more votes in the Democratic stronghold of Cook County than the conservative Republican gubernatorial nominee state Sen. Bill Brady did in his contest against the Democrat Pat Quinn. Kirk won his race, while Brady lost.

For this campaign, Kirk has the backing Americans for Responsible Solutions, the anti-gun violence PAC founded by former congresswoman Gabby Giffords and her husband and the LGBT rights group Human Rights Campaign.

But this time around it will be even more difficult for Kirk to thread the needle as he tries to appeal to independents turned off by Trump, while keeping staunch Trump supporters on his side, said Brian Gaines, a political scientist at the University of Illinois at Urbana-Champaign.

“If the election were held today, he’d probably lose it,” Gaines said. ”At this point, the Trump shadow on the race is scaring Republicans. No one thought Trump could be competitive in this state, but there’s more of a sense that his presence can cause backlash downballot.”

After a campaign event here, Kirk backer Terry Ferguson noted that another Illinois GOP lawmaker, Rep. Rodney Davis, was getting hammered on social media by Trump supporters for withdrawing his endorsement for the GOP presidential nominee after the leak of the Access Hollywood video in which Trump can be heard talking about forcing himself on women.

But Ferguson, a farmer from Clinton, Ill. who heads Farmers for Kirk, said he was hopeful that Trump supporters will stick by the senator’s side.

“Maybe it will help him that he took his position on Trump a while ago,” Ferguson said. “Everybody knew Mark’s position from the get-go.”

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On the campaign trail, Kirk said he’s gotten plenty of questions about Trump. But he says most voters are accepting of his position.

After an event last week with college Republicans at Illinois Wesleyan University, Kirk told reporters he was optimistic that the Republican Party will work to remind Americans that it’s the “party of fiscal conservatives and national security hawks.”

He insists that Trump won’t be an anchor on his or other Republicans candidates downballot. That said, he had a hard time hiding his disdain for his party’s candidate at the top of the ticket.

“Right now I would tell Trump to shut the hell up,” Kirk said. “This is not productive.”

Follow USA TODAY Chicago correspondent Aamer Madhani on Twitter: @AamerISmad

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