(CNN) - The Democrats have a slight lead in two crucial Senate showdowns that could decide whether the party keeps control of the chamber this November, according to new polling.
And NBC News/Marist surveys released Tuesday also indicate that two important gubernatorial races are all knotted up.
According to the poll, Democratic Sen. Mark Udall of Colorado leads his GOP challenger, Rep. Cory Gardner, 48%-41%, among registered voters, with one in ten undecided. In the state's gubernatorial contest, Democratic Gov. John Hickenlooper has a 49%-43% edge over Republican challenger Bob Beauprez, a former congressman. Seven percent are undecided.
In the Senate race in Michigan, the poll indicates that Democratic Rep. Gary Peters has a 43%-37% edge over Republican candidate Terry Lynn Land, a former Michigan secretary of state, with a high 19% undecided. The winner in November will succeed longtime Democratic Sen. Carl Levin of Michigan, who is retiring. In the gubernatorial contest, GOP Gov. Rick Snyder holds a 46%-44% margin over Democratic nominee Mark Schauer, with 9% undecided.
Democrats have a 55-45 majority in the Senate (53 Democrats and two independents who caucus with the party). But in the midterms, the party is defending 21 of the 36 seats up for grabs, with half of those Democratic-held seats in red or purple states.
"The early edge goes to the Democrats" said Lee Miringoff, the director of the Marist College Institute for Public Opinion. "But these are not states they can put into their win column just yet."
When it comes to governors' races, the Republicans are defending 22 of the 36 seats up for grabs in November. And some of them are in states that Obama carried in both 2008 and 2012, such as Michigan, as well as Pennsylvania, Ohio, Wisconsin, Florida, Maine, Nevada and New Mexico. But Democrats also have some vulnerable seats to defend, in Colorado, as well as Arkansas and Illinois. And they won't have cakewalks in Connecticut and Massachusetts.
In the Senate races, the poll indicates that a gender gap is helping the Democrats. Udall tied up with Gardner among male voters, but is up by 12-percentage points among females. In Michigan, Peters' holds a 13-point lead over his female opponent among women voters.
In Colorado, big leads among Latino voters are helping Udall and Hickenlooper.
The GOP candidates appear to be getting a lift from perceptions about President Barack Obama, and the Affordable Care Act, better known as Obamacare. Fifty-two percent of Colorado voters and half of Michigan voters say they view the national health care law as a bad idea. And while the President carried both states in the 2012 election, Obama's approval rating in both states now stands at 40%. Republicans are trying to frame the midterms as a referendum on the President and Obamacare.
The NBC News/Marist polls were conducted July 7-10, with 914 registered voters in Colorado and 870 registered voters in Michigan questioned by telephone. The Colorado survey had a sampling error of plus or minus 3.2 percentage points. The Michigan poll had a sampling error of plus or minus 3.3 percentage points.
CNN Political Editor Paul Steinhauser contributed to this report