Democrats and Republicans are running neck and neck in Nevada’s key contests for U.S. Senate and governor, according to a new NBC News/Marist poll of the state released Tuesday, four weeks before Election Day.

In the Senate race — one of the Democrats’ best pick-up opportunities in their bid to win control of that chamber — incumbent Republican Sen. Dean Heller gets support from 46 percent of likely voters, while Democratic challenger Jacky Rosen gets 44 percent.

When the matchup is expanded to include the Libertarian candidate and “none of these candidates,” which is an option on the Nevada ballot, Heller continues to lead by 2 points, 44 percent to 42 percent.

Both results are well within the poll’s margin of error of plus-minus 5.5 percentage points for likely voters.

“This is the only Senate contest in the nation where a Republican is seeking re-election in a state Hillary Clinton carried in 2016,” said Lee Miringoff, director of the Marist College Institute for Public Opinion, which conducted this poll. “But it’s still anybody’s guess whether Nevada can boost the Democrats’ chances of achieving a Senate majority or break them.”

Inside the head-to-head numbers, Heller leads among likely Republican voters (90 percent to 5 percent), men (54 percent to 38 percent), whites (48 percent to 44 percent) and independents (42 percent to 39 percent).

Rosen, meanwhile, has the advantage with Democrats (89 percent to 8 percent), Latinos (54 percent to 38 percent) and women (50 percent to 39 percent).

Rosen is ahead in Clark County (Las Vegas) by 11 points, 50 percent to 39 percent. But Heller leads by 26 points in Washoe County (Reno), 60 percent to 34 percent.

In the gubernatorial contest, Republican Adam Laxalt gets support from 46 percent of likely voters, compared with 45 percent for Democrat Steve Sisolak. When the ballot is expanded to include the Libertarian candidate and “none of these,” Laxalt’s advantage grows to 4 points, 44 percent to 40 percent.

Despite these narrow leads for Republicans, the poll does provide some encouraging news for Democrats. For one thing, they’re more enthusiastic – 89 percent of likely Democratic voters in Nevada say they consider this year’s midterm elections “very important,” compared with 82 percent of state Republicans who agree.

In addition, the sliver of persuadable voters — those who are undecided, leaning toward a candidate and might vote differently on Election Day — are more negative about President Donald Trump than the electorate at large, and they tend to prefer Democrats in charge of Congress.

Trump’s approval rating in Nevada: 45 percent

President Trump’s overall job rating among likely voters stands at 45 percent approve, 47 percent disapprove, the NBC/Marist poll finds.

Among the larger pool of registered voters, it’s 43 percent approve, 47 percent disapprove. (Among persuadable voters, Trump’s approval rating is below 30 percent.)

Republicans hold a 2-point lead in congressional preference in Nevada, with 47 percent of likely voters preferring a GOP-controlled Congress, versus 45 percent who want the Democrats in charge. (Persuadable voters prefer a Democratic-controlled Congress by double digits.)

But by a 51 percent-to-39 percent margin, likely voters in Nevada say their 2018 vote will be to send a message for more Democrats to serve as a check and balance on Trump, rather than more Republicans who will help the president pass his agenda.

As for the top issue that might factor into their voting decision, 26 percent of likely voters say it’s the economy and jobs; 25 percent say it’s health care; 18 percent say it’s immigration; and 9 percent say taxes and spending.

Voters divided on Kavanaugh

And finally, the NBC/Marist poll finds 38 percent of likely voters saying they’re more likely to vote for a candidate who supported Trump’s Supreme Court nominee Brett Kavanaugh, who won confirmation to the nation’s highest court on Saturday.

That’s compared with 41 percent of voters who say they’re more likely to vote for a candidate who opposed Kavanaugh. Eighteen percent say the issue doesn’t matter to their vote.

In Nevada’s Senate race, Heller voted for Kavanaugh’s confirmation to the Supreme Court, while Rosen opposed it.

The NBC/Marist poll of Nevada was conducted – via interviews by landline and mobile phones – Sept. 30 to Oct. 3 of 929 adults (which has a margin of error of plus-minus 4.2 percentage points), 780 registered voters (plus-minus 4.5 percentage points) and 574 likely voters (plus-minus 5.5 percentage points).