Sen. Joe Donnelly Joseph (Joe) Simon DonnellyTrump meets with potential Supreme Court pick Amy Coney Barrett at White House Names to watch as Trump picks Ginsburg replacement on Supreme Court Momentum growing among Republicans for Supreme Court vote before Election Day MORE (D-Ind.) holds a slight six-point lead over opponent Mike Braun in Indiana’s Senate race, according to a new NBC News/Marist poll released Wednesday.

The poll finds Donnelly has the support of 49 percent of likely voters, while Braun is backed by 43 percent of likely voters. Among registered voters Donnelly led Braun by 48-42.

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Donnelly's lead over Braun is narrowed to three points when including Libertarian candidate Lucy Brenton.

Donnelly is one of ten Democratic senators running for reelection in states President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE won in 2016, and he is considered one of that group’s most vulnerable candidates.

He'll face Braun, a former state representative and a businessman, in November.

Indiana voted for Trump by nearly 20 points. The president currently has a positive approval rating of 48 percent, the NBC News/Marist poll also found, compared to 46 percent who disapprove among likely voters.

However, among all adults, 47 percent disapproved of Trump's performance, while 44 percent approved.

Donnelly himself had a 48 percent approval rating among likely voters, compared to 31 percent who had a negative view.

Braun, by contrast was less known. Approximately 39 percent of likely voters approve of Braun, compared to 32 percent who disapprove. However, 29 percent have not heard enough about him to have an opinion.

Furthermore, among Indiana's likely voters, 49 percent said they wanted Democrats in Congress to act as a check and balance against Trump, while 42 percent said they would prefer more Republicans who will help Trump with his agenda.

The Cook Political Report rates the race as a “toss up.”

Republicans currently have a 51-49 majority in the Senate and are hoping their favorable map will help overcome an energized Democratic base in a midterm election cycle largely considered to be a referendum on the president.

NBC News and Marist interviewed 955 Indiana adults, including 576 likely voters, from Aug. 26-29. The poll has a margin of error of +/- 3.9 percent for all adults and +/- five percent for all likely voters.