Why did Sen. Mark Kirk even bother to run for re-election?

The Illinois Senate race pitting the incumbent Republican against Democratic Rep. Tammy Duckworth is one of the most bizarrely fascinating spectacles of the year, largely because it’s not exactly clear who Kirk is supposed to appeal to. In many ways, Kirk is the equivalent of a songwriter who composes tunes only he can understand.

Back in June 2009, then-Rep. Kirk was one of the eight courageous Republicans who voted in favor of the Waxman-Markey climate bill. Rather than continue to defend his brave action in the face of vicious right-wing criticism, Kirk abandoned all concern for the climate as he pursued the US Senate seat once held by President Obama; after defeating Democrat Alexi Giannoulias in November 2010, he had the nerve to suggest that the breakdown of Al Gore’s marriage impacted the former Vice President’s credibility on carbon control.

By early-2015, perhaps realizing that the political will to take action on climate had only grown stronger over the past half-decade, Kirk attempted to reclaim his past rationality on this issue, voting in favor of a Democratic-sponsored amendment affirming that human-caused climate change is real and co-founding the Senate Energy and Environment Working Group to consider ways to advance the cause of clean energy. The problem is, Kirk’s credibility on the environment remains shaky:

Illinois’ Kirk — who is up against Rep. Tammy Duckworth (D-IL), a lawmaker a lifetime score of 85 percent on the environment from the League of Conservation Voters — has publicly waffled on his views on climate change, though his support of Graham’s amendment suggests that he now is of the position that climate change is both real and caused, at least in part, by human activity. His voting track record, however, is less than stellar: In 2015, he voted to overturn the Clean Water Rule, which would protect the water of nearly a third of Americans, and voted numerous times to approve the Keystone XL pipeline. Kirk did break with party lines over the Clean Power Plan, however, voting against Sen. Mitch McConnell’s (R-KY) resolution that sought to block the EPA’s carbon pollution standards for new and existing power plants, which have been viewed by many as the cornerstone of President Obama’s domestic climate policy.

Kirk simply cannot appeal to both moderates and conservatives at the same time–on climate or any other issue. His relative rationality on LGBT issues may have earned him the support of the Human Rights Campaign, but those fighting for full equality on LGBT issues cannot overlook his continued affiliation with a party that believes only straight people are morally decent. His decision to simultaneously embrace and reject Republican presidential nominee Donald Trump is, for want of a better word, crazy. In addition, his cordiality towards Supreme Court nominee Merrick Garland means nothing when his party still refuses to even hold confirmation hearings for the highly regarded judge.

If Kirk loses by a significant margin on November 8, he’ll go down in history next to Scott Brown as yet another prominent blue-state Republican Senator who had no natural constituency. Will he try to blame Trump in his concession speech? If so, will he be laughed right out of the room?

UPDATE: More from Steve Benen and Chris Hayes.

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D. R. Tucker is a Massachusetts-based journalist who has served as the weekend contributor for the Washington Monthly since May 2014. He has also written for the Huffington Post, the Washington Spectator, the Metrowest Daily News, investigative journalist Brad Friedman's Brad Blog and environmental journalist Peter Sinclair's Climate Crocks.