Arizona’s closely watched Senate race to replace retiring Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeHow fast population growth made Arizona a swing state Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden MORE (R) is neck and neck between Reps. Kyrsten Sinema (D) and Martha McSally Martha Elizabeth McSallyThe Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' New ABC/WaPost poll finds Trump edging Biden in Arizona, Florida MORE (R) according to a new NBC News/Marist poll released Tuesday.

In the survey, Sinema has the support of 48 percent of likely voters, while 45 percent back McSally, a 3-point difference that falls within the poll’s margin of error.

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The poll also shows that Green Party candidate Angela Green could sway the election.

When Green is included in the polling, Sinema’s support slips to 45 percent among likely voters, while McSally’s falls to 43 percent and Green is backed by 6 percent of likely voters.

Sinema holds a double-digit lead among independents, whites with a college degree, Hispanics and women, while McSally maintains strong support among Trump supporters, men and whites without a college degree.

Sinema has a net-positive favorability rating among Arizona likely voters.

About 46 percent of respondents have a positive view of her, compared to 33 percent who view her unfavorably.

McSally has a net-negative favorability rating, with 40 percent of Arizona respondents viewing her favorably and 42 percent unfavorably.

McSally, who attempted to tie herself closely to President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE during a brutal GOP primary, could be being dragged down by his net-negative job approval rating. About 44 percent of likely Arizona voters approve of the job Trump’s doing, while 51 percent disapprove.

Trump backed McSally in August, tweeting, "Martha McSally is an extraordinary woman. She was a very talented fighter jet pilot and is now a highly respected member of Congress. She is Strong on Crime, the Border and our under siege 2nd Amendment. Loves our Military and our Vets. Has my total and complete Endorsement!"

Martha McSally is an extraordinary woman. She was a very talented fighter jet pilot and is now a highly respected member of Congress. She is Strong on Crime, the Border and our under siege 2nd Amendment. Loves our Military and our Vets. Has my total and complete Endorsement! — Donald J. Trump (@realDonaldTrump) August 29, 2018

About 52 percent of Arizona likely voters said they would vote for Democrats to be a check and balance on Trump, while 38 percent said their vote would be a message in favor of more Republicans to help Trump pass his agenda.

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

The NBC News/Marist poll surveyed 564 likely voters from Sept. 16-20 and has a margin of error of 4.7 percentage points.