To quote Irving Berlin:
"Oh I wish and wish and wish again,
That I was back home there in Michigan..."
Republicans did this numerous times in Michigan to Dems, and once, and threw the primary to pre-reformed bigot George Wallace and we all know how that went:
In 1972, Republican voters in Michigan decided to make a little mischief, crossing over to vote in the open Democratic primary and voting for segregationist Democrat George Wallace, seriously embarrassing the state's Democrats. In fact, a third of the voters (PDF) in the Democratic primary were Republican crossover votes. In 1988, Republican voters again crossed over, helping Jesse Jackson win the Democratic primary, helping rack up big margins for Jackson in Republican precincts. (Michigan Republicans can clearly be counted on to practice the worst of racial politics.) In 1998, Republicans helped Jack Kevorkian's lawyer -- quack Geoffrey Feiger -- win his Democratic primary, thus guaranteeing their hold on the governor's mansion that year.
I love a bit of turnabout, just rewards, taste of their own medicine, don't you?