As Michigan residents head to the polls, native son Mitt Romney and ex-Pennsylvania Sen. Rick Santorum have a lot on the line.
Losing the state he grew up in would be a blow to Romney's campaign, but Santorum's banking big on a strong Michigan showing to build momentum heading into next week's Super Tuesday contests.
Voters who select a GOP presidential ballot Tuesday also can choose Newt Gingrich or Ron Paul. Seven Republicans on the ballot are inactive or haven't mounted major campaigns.
President Barack Obama has no competition in the Democratic primary, and votes for him won't count. Democrats will choose theirfavorite at a May 5 caucus.
Romney, Santorum and Paul have campaigned heavily.
At stake for Republicans are 30 delegates awarded largely by congressional district.