Within hours of President Trump apologizing to Justice Brett Kavanaugh and his family “for the terrible pain and suffering” inflicted on Kavanaugh during the contentious confirmation fight, embattled Sen. Joe Donnelly, D-Ind., defended his opposition to Kavanaugh.

During a Monday night debate at Purdue University, the first-term incumbent claimed he “voted against Judge Kavanaugh because of concerns about his impartiality and apprehensions about his judicial temperament.” Not so, businessman and Republican challenger Mike Braun countered: “Democrats including Joe Donnelly will do or say anything when it comes to their political interests. It is a blood sport.”

Donnelly doesn’t know it yet, but his “judicial temperament” dodge will soon become an epic political blunder.

By claiming Kavanaugh’s supposed hot temper and purported lack of impartiality motivated his vote, Donnelly tacitly acknowledged the Supreme Court justice is innocent of the last-minute sexual misconduct charges levied against him. After all, if Donnelly believed Kavanaugh guilty of sexual assault, why take refuge in the much less disturbing question of judicial demeanor?

Yet, Donnelly remains silent about his liberal colleagues’ decision to weaponize Christine Blasey Ford’s discredited sexual assault allegations. Donnelly’s refusal to condemn the vile attacks on Kavanaugh only serves to reinforce Republican challenger Braun’s charge that the Indiana Democrat “takes his marching orders” from Senate Minority Leader Chuck Schumer, D-N.Y.

Donnelly’s acquiescence in the attempted character assassination of the married father of two leaves him at risk when Hoosiers head to the polls in less than a month. With recent polls showing 87 percent of Republicans, 26 percent of Democrats, and 58 percent of Independents disapprove of Senate Democrats’ handling of Kavanaugh’s confirmation hearing, Donnelly’s vote and his justification for it leave him clinging to a 2 percentage point lead in the polls.

But those polls may not capture the true sentiments in this midwestern battleground state which saw Trump defeat Hillary Clinton two years ago by nearly 20 percentage points. Recognizing this reality, Donnelly used his first debate against Braun to position himself as a bipartisan moderate, calling the late John McCain, “My friend, my mentor, my hero in politics.” Then, hearkening back to McCain’s motto when the Arizona senator ran for president, “Country First,” Donnelly professed “that’s what this should be about.”

Donnelly’s attempt to increase his bipartisan gravitas by calling on the maverick spirit of McCain might play well in Indiana under different circumstances. But on the heels of the Kavanaugh inquisition, “Party First,” seems more apropos for Donnelly.

By invoking McCain’s memory, the Indiana senator has also unwittingly set himself up for a repeat of one of the most devastating political punches ever thrown, when Sen. Lindsey Graham, R-S.C., keeps his promise to take what the Democrats did to Kavanaugh “to the streets, at the ballot box.” Vowing to do something he has never done before (campaign against a colleague), Graham holds the perfect rejoinder to Donnelly’s claimed independence:

“Senator, I served with John McCain for 15 years. I knew John McCain. John McCain was a close friend of mine. Senator, you’re no John McCain.”

Graham’s fiery performance on the Judiciary Committee made headlines when he unbraided Democrats and told his colleagues, “If you vote no, you are legitimizing the most despicable thing I’ve ever seen in my time in politics.” While left-leaning pundits put Graham’s harsh words down to the absence of McCain’s mediating presence, McCain’s anger “would have made me look like a choir boy,” Graham said, remembering his dear friend.

With Graham poised to enter the midterm fray for the first time, Donnelly’s decision Monday evening to sidestep the outrage surrounding the Kavanaugh confirmation battle and instead cloak himself in McCain’s mantle of moderation may well prove a career-ending move.

Margot Cleveland (@ProfMJCleveland) is a contributor to the Washington Examiner's Beltway Confidential blog. She served nearly 25 years as a permanent law clerk to a federal appellate judge, and is a former full-time faculty member and current adjunct professor for the college of business at the University of Notre Dame.