Democratic Senate candidates are leading in three key battleground states as the party looks to defend a difficult map ahead of the November midterm elections, according to new polls.

Arizona Rep. Kyrsten Sinema (D) and Ohio Sen. Sherrod Brown Sherrod Campbell BrownHarris faces pivotal moment with Supreme Court battle Remote work poses state tax challenges Senate Democrats release report alleging Trump admin undermined fair housing policies MORE (D) are both leading their GOP challengers by double digits, while Florida Sen. Bill Nelson Clarence (Bill) William NelsonDemocrats sound alarm on possible election chaos Trump, facing trouble in Florida, goes all in NASA names DC headquarters after agency's first Black female engineer Mary W. Jackson MORE (D) is up by just 4 points, about the margin of error in the new NBC News/Marist polls released Tuesday evening.

The results show how some of the major Senate races this cycle are shaping up with less than five months until Election Day.

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In Arizona, Sinema has mounted a strong candidacy that's unified the party as several Republican candidates continue to battle ahead of their primary Aug. 28.

Brown continues to hold a significant lead in Ohio as Rep. Jim Renacci James (Jim) B. RenacciOhio is suddenly a 2020 battleground Democrats fear Ohio slipping further away in 2020 Medicare for All won't deliver what Democrats promise MORE (R) has struggled to close the gap after winning his own primary in early May.

And the Florida battle between Nelson and the state's deep-pocketed Republican Gov. Rick Scott is expected to be one of the premier races in the country — as well as one of the costliest.

As the presumptive Democratic nominee, Sinema leads Rep. 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), the frontrunner in the Arizona GOP primary, by 11 points in the new poll. Former state Sen. Kelli Ward trails Sinema by 10 points, while former Maricopa County Sheriff Joe Arpaio is behind the Democrat by 25 points.

McSally leads the crowded primary field with 30 percent to Ward's 28 percent, with Arpaio sitting in third with the support of 21 percent of respondents.

Democrats are bullish on flipping the Arizona seat being vacated by 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) — Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE only lost the state by 4 points in 2016 and the party believes a combination of strong turnout and lengthy GOP primary will help them in the fall.

Republicans have sought to counter that enthusiasm by arguing that the race will narrow once the party coalesces around a candidate, pointing to the deep-red history of the state.

In Ohio, the NBC poll shows Brown leading Renacci by 13 points in a state where Republicans came into the cycle confident they could knock off the longtime incumbent.

So far, public polling shows Brown leading by double-digits, and while Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellFEC flags McConnell campaign over suspected accounting errors Poll: 59 percent think president elected in November should name next Supreme Court justice Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ky.) recently told The Hill he's more confident about his party's chances in the state, he also left the state off his list of top targets during an interview with The Wall Street Journal.

Nelson's 4-point lead in Florida, 49 percent to 45 percent, is good news for a campaign that's seen the race tighten since Scott officially launched his bid in April.

Scott has shown a willingness to spend his vast personal wealth on his political bids, only adding to the likelihood that the race will become one of the most expensive on the Senate map this year.

Democrats have taken aim at Scott's at times polarizing tenure leading the state, as well as his friendliness to President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE. But Republicans see Nelson as beatable and have begun to rough him up in the weeks after Scott announced his bid.

The Arizona poll reached 839 registered voters between June 17-21 with an overall margin of error of 4.5 percentage points and a margin of error of 6.7 percentage points for the 371 Republican primary voters polled.

The Florida survey of 947 registered voters contacted during the same period has a margin of error of 3.9 percentage points.

In Ohio, the poll surveyed 778 registered voters between June 17-22 with a margin of error of 4.4 percentage points.