(CNN) - U.S. Senate races in Kansas and Missouri and a ballot measure seen as a referendum on President Obama's health care reform highlighted Tuesday's primary elections.
Missouri's Proposition C allowed Missouri voters to decide if residents should be allowed to opt out of mandatory health insurance - a key part of the administration's health care plan.
The measure succeeded handily, winning by a three to one margin to allow residents to opt out.
Ahead of the vote, Mason-Dixon pollster Brad Coker told the St. Louis Post-Dispatch that he expected the proposition to pass because of an anticipated heavier Republican turnout.
But he also expects a court challenge.
Some states have already passed similar legislation, but this was the first test at the ballot box.
Elsewhere in Missouri, there wasn't as much drama in the fight to succeed retiring Republican Sen. Kit Bond.
Missouri Secretary of State Robin Carnahan, who hails from one of the state's leading political dynasties, easily won the Democratic primary.
Rep. Roy Blunt, the former House Majority Whip, manhandled a nine-candidate Republican field.
The GOP Senate battle was the marquee race in Kansas, as two congressmen fought to replace fellow Republican Sen. Sam Brownback, who ran for governor rather than for re-election.
Rep. Jerry Moran narrowly defeated Rep. Todd Tiahrt, who made a late charge in the race with the endorsement of Sarah Palin and Tea Party backers.
Baker University administrator Lisa Johnston defeated a field of five Democratic candidates, but Moran will be considered the overwhelming favorite in the general election, because Kansas hasn't put a Democrat in the Senate since 1932.
"The winner of the Republican primary essentially becomes the winner in November because Kansas is a state where Republicans dominate in federal races," said Nathan Gonzales, political editor for the nonpartisan Rothenberg Report.
Brownback, who made a bid for the White House in 2008, won the GOP gubernatorial nomination and will face State Sen. Tom Holland, who had no opposition in the Democratic primary, in November.
In Michigan, the state with the second highest unemployment level in the country, the contest for the GOP gubernatorial nomination was the headliner.
Businessman and former Gateway CEO Rick Snyder defeated powerful Rep. Peter Hoekstra, the senior Republican on the House Intelligence Committee, and Attorney General Mike Cox in what was a three-way battle.
Snyder will face Lansing Mayor Virg Bernero who won the Democratic nomination over State Rep. Andy Dillon. Two-term Democratic Gov. Jennifer Granholm is term-limited.
With Michigan's economy continuing to sputter and with a sitting Democratic president and an outgoing Democratic governor, "it looks like Michiganders might be willing to let Republicans have a shot at governing," said Gonzales.
The GOP also is hoping to score a pickup in November in Michigan's 1st Congressional District, where longtime Democratic Rep. Bart Stupak announced in April that he would not run for re-election after being battered for changing his no vote on health care to a key yes vote.