New results from NBC News/Marist polls show close races in midterm contests that will decide control of the U.S. Senate.

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The polls found momentum in most of the races has swung to the Republicans, however.

Colorado:

Rep. Cory GardnerCory GardnerGun control group alleges campaign finance violations in lawsuit against NRA Colorado Supreme Court signs off on new congressional map Colorado remap plan creates new competitive district MORE (R) holds a slim lead over Sen. Mark UdallMark Emery UdallKennedy apologizes for calling Haaland a 'whack job' OVERNIGHT ENERGY: Haaland courts moderates during tense confirmation hearing | GOP's Westerman looks to take on Democrats on climate change | White House urges passage of House public lands package Udalls: Haaland criticism motivated 'by something other than her record' MORE (D), 46 to 45 percent. In September, the incumbent led 48 to 42 percent.

Iowa:

Joni Ernst leads Rep. Bruce BraleyBruce Lowell BraleyFormer lawmakers sign brief countering Trump's claims of executive privilege in Jan. 6 investigation The Memo: Trump attacks on Harris risk backfiring 2020 caucuses pose biggest challenge yet for Iowa's top pollster MORE (D), 49 to 47 percent. Her lead was 2 percentage points, 46 to 44 percent, earlier this month.

Kansas:

Greg Orman (I) holds a slight lead over Sen. Pat RobertsCharles (Pat) Patrick RobertsMcConnell gets GOP wake-up call Bob Dole, Pat Roberts endorse Kansas AG Derek Schmidt for governor Ex-Sen. Cory Gardner joins lobbying firm MORE (R), 45 to 44 percent. Orman was up 10 points earlier this month.

Arkansas:

Rep. Tom CottonTom Bryant CottonGraham emerges as go-to ally for Biden's judicial picks China draws scrutiny over case of tennis star Peng Shuai Biden says he's 'considering' a diplomatic boycott of Beijing Olympics MORE (R) has a 2-point lead over Sen. Mark PryorMark Lunsford PryorBottom line Everybody wants Joe Manchin Cotton glides to reelection in Arkansas MORE (D), 45 to 43 percent. Cotton held a 5-point lead last month.

North Carolina:

The new NBC News/Marist poll shows Sen. Kay HaganKay Ruthven HaganInfighting grips Nevada Democrats ahead of midterms Democrats, GOP face crowded primaries as party leaders lose control Biden's gun control push poses danger for midterms MORE (D) deadlocked with Republican opponent Thom Tillis, with each candidate taking 43 percent support. Libertarian Sean Haugh takes 7 percent. Hagan had a 4-point lead earlier this month.

All the races are within the polls’ margins of error.

Pollster Barbara Carvalho of Marist College’s Institute for Public Opinion said, unlike 2012, “Democrats are now struggling to protect their firewall in Iowa, North Carolina and Colorado.”