(CNN) - Democratic Sen. Claire McCaskill of Missouri now has the Republican challenger she'd hoped for, but the first term senator still faces a serious fight to keep her seat in November.
It appears to be a different story in Michigan, where Democratic Sen. Debbie Stabenow's re-election prospects after Tuesday's primary continue to look strong against GOP attempts to defeat her in the general election.
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In Missouri, Rep. Todd Akin came from behind in a crowded field of candidates in the Senate Republican primary to defeat two opponents who were polling above him in the most recent surveys, wealthy businessman John Brunner and former state Treasurer Sarah Steelman.
Akin may have had an assist from the Democrats. In the past few weeks, the McCaskill campaign and the Democratic Senatorial Campaign Committee ran ads slamming Akin for being too conservative on social issues, knowing full well that the spots would only benefit the six-term congressman among the conservative primary electorate.
"Akin's nomination may just be a sliver of good news for Democrats, though. McCaskill has been firmly lodged in the low to mid-40s in general election ballot tests for months- a dangerous place for an incumbent, although she performed slightly better against Akin than the other two Republicans," writes Jessica Taylor, senior analyst for the non-partisan Rothenberg Political Report.
A Mason-Dixon poll conducted late last month for the St. Louis Dispatch indicated Akin with a 49%-44% advantage over McCaskill in a November showdown.
Former Rep. Pete Hoekstra cruised to victory in Michigan's Republican Senate primary, beating charter schools executive Clark Durant, who grabbed the support of some leading conservative groups the past couple of weeks.
"The outcome doesn't improve Republican prospects in the Wolverine State," adds Taylor. "Neither candidate had polled very closely against Sen. Debbie Stabenow (D), and with better GOP pickup opportunities in other states, don't expect either party to invest money here."
The Democrats currently hold a 53-47 advantage in the Senate, but they are defending 23 (21 Democrats and two independents who caucus with the party) of the 33 seats up for grabs in November.
Of the two states, Missouri seems more important to GOP hopes for winning back control of the chamber.
"Republicans don't need to win Michigan for a majority but they have to have Missouri. Democrats are ecstatic to face Akin, but McCaskill is an incumbent who has had trouble getting above 45 percent in the polls for months," Rothenberg Report Deputy Editor Nathan Gonzales tells CNN.
The Rothenberg Report rates the Missouri race as "toss up/tilt Republican" and the Michigan race as "Democrat favored."
Another top non-partisan political handicapper, the Cook Political Report, rates the Missouri contest as a "toss up" with the Michigan race "leaning Democrat."
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