In a forthright message to supporters, U.S. Sen. Dick Lugar, R-In., argues the seat will fall out of Republican hands if voters elect state Treasurer Richard Mourdock in the upcoming GOP primary.The 36-year-incumbent faces the end of his political career on Tuesday with Mourdock up by 10 points in a new independent poll. Mourdock is backed by the Tea Party, and several high-profiled conservatives such as former Alaska Governor Sarah Palin and former Republican presidential candidate Rick Santorum.But Lugar says if Hoosiers give Mourdock the nomination then the Democrats will not only win the seat, but maintain their majority in the Senate this fall.From the Lugar campaign: Independent polls show that I would beat the Democratic challenger, Joe Donnelly, by more than 20 points. Independent polls also show that my Republican opponent, Richard Mourdock, would not. For that reason, both state and national Democrats, including Super-PACs, have been pouring money into the state trying to get Richard Mourdock elected. Democrats understand Joe Donnelly will beat Richard Mourdock. Not only would a Joe Donnelly victory mean that Indiana would be represented by a man who supported Obamacare and Obama's stimulus, but it would also give Democratic Party Majority Leader Harry Reid another vote in the Senate. This is serious. Losing our Indiana Senate seat to the Democrats is not a risk that Republicans can take.The GOP needs to pick up four seats to take control of the Senate and Indiana was considered a safe Republican seat a few months ago. However, a poll conducted in March showed Donnelly and Mourdock tied, and the Democratic nominee is taking early shots at the Tea Party challenger.Political observers note Donnelly has had poor fundraising numbers and say he will have an uphill battle regardless of who wins the nomination. But a Mourdock victory would make the race much closer than originally anticipated and energize Democrats.The Indiana primary is May 8.