(Reuters) - During the U.S. Senate debate in Indiana on Monday, it was difficult at times to tell which candidate was the Democrat and which the Republican, as both routinely cited their support of President Donald Trump’s agenda.

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For incumbent Democratic Senator Joe Donnelly, that reflected the fact that he will need the president’s supporters to win reelection in a state that overwhelmingly supported Trump two years ago.

Donnelly, a first-term senator, is trying to stave off a challenge from Republican businessman Mike Braun, and in doing so, keep alive Democratic hopes of taking control of the U.S. Senate after the Nov 6. congressional elections.

Democrats need a net gain of two Senate seats to take a majority in the upper chamber, which would allow them to more effectively counter Trump’s agenda. But doing that not only means winning at least two seats now held by Republicans, but also holding onto seats in conservative states that Trump won, including Indiana, Montana, North Dakota and West Virginia.

Donnelly has spent much of his campaign touting his record working with Trump on healthcare and veterans’ issues. But he came under attack by Braun on Monday for his opposition to the confirmation of Supreme Court Justice Brett Kavanaugh.

Braun charged Donnelly was doing the political bidding of liberal Democrats such as Senate Minority Leader Chuck Schumer. “He never sticks his neck out,” Braun said of Donnelly.

Senator Joe Manchin of West Virginia, facing his own reelection fight, was the only Democrat to back Kavanaugh, who was accused of sexual assault while a teenager.

Donnelly said he voted against Kavanaugh because of “concerns about his impartiality and concerns about his judicial temperament,” apparently referring to the emotional defense Kavanaugh mounted to senators before the confirmation vote.

Donnelly also played up his support last year of Trump’s first Supreme Court pick, Neil Gorsuch, and noted that he had voted in favor of Trump’s agenda more than 60 percent of the time.

“I support President Trump’s efforts,” Donnelly said during the debate. “I want him to be successful. Because when a president is successful that means the United States is successful. That’s what this is supposed to be about.”

Donnelly even went as far as to adopt the slogan “Promises Made, Promises Kept” used by Trump’s reelection campaign as his own motto during his closing statement. It is a phrase commonly employed by Vice President Mike Pence, a former Indiana governor, at campaign events.

Braun, the owner of a logistics company who modeled his own outsider candidacy after Trump’s presidential bid, noted that Donnelly had not supported Trump’s tax-cut plan in the Senate and was an ardent backer of the Affordable Care Act, former Democratic President Barack Obama’s signature domestic achievement, which Trump has sought to repeal.

Donnelly has tried to walk a fine line all year. He supported the tariffs that Trump slapped on steel and aluminum imports, saying they benefited Indiana industry, but then opposed tariffs that resulted in retaliation by China that hurt the state’s farmers.

That may be one reason why most polls have shown him holding a slight lead over Braun, who has struggled with name recognition and finding a viable line of attack against Donnelly.

If Monday’s debate was any sign, Braun believes he has found that in the controversy over Kavanaugh, although he must hope that it still lingers in voters’ minds a month from now.