WASHINGTON (Detroit Free Press) -- American Crossroads, one of the largest conservative Super PACs in the country, on Friday released a series of polls it had commissioned, including one showing former Michigan Secretary of State Terri Lynn Land with a slight lead over U.S. Rep. Gary Peters in the race for the U.S. Senate.

The survey - an automated telephone poll done by Harper Polling on Jan. 19-20, when 750 likely voters were contacted - showed Land, the only well-known Republican to enter the race, leading Peters, the presumptive Democratic nominee, 42% to 37%, with 21% undecided.

The margin of error was plus or minus 3.6 percentage points. Land's lead was slightly less than the 44%-36% lead Harper reported in an earlier poll conducted in January with another group. A Rasmussen Reports poll done in January showed Land ahead by 2 points, well within that poll's 4.5 percentage point margin of error.

The new poll comes as groups outside the campaigns have mounted efforts that could have an effect on the race: Last month, Americans for Prosperity, which supports conservative causes, launched a million-dollar ad campaign criticizing Peters' support of the Affordable Care Act.

While the Free Press often does not release polls commissioned by groups that may have a rooting interest in the outcome, the inclusion of the Michigan race by American Crossroads could be another sign that conservatives increasingly believe the seat is up for grabs. It could also potentially signal the interest of a powerful player on the national scene in the contest.

Michigan Democrats criticized the poll as overestimating the sample size from Land's home region in the Grand Rapids area and underestimating that in the Detroit media market, where Peters, D-Bloomfield Township, has served three terms in Congress.

No Republican Senate nominee in Michigan has won since 1994, but if the party could somehow wrest the seat - currently held by U.S. Sen. Carl Levin, who is retiring - from Democratic control, it could go a long way toward securing a majority in the Senate chamber.

As a Super PAC, American Crossroads, linked to political adviser Karl Rove, was among the top spenders in the 2012 elections and is expected to be a big player in this year's midterms. Super PACs can raise and spend unlimited sums but must work independently of candidate committees.

Of the eight Senate race polls released by American Crossroads, only one other - in New Hampshire - involved a state that, like Michigan, supported President Barack Obama in 2012.

Contact Todd Spangler: 703-854-8947 or at