The experienced, moderate Indiana Senator looks likely to lose in the primaries to a Tea Party challenger. Kornacki explains the importance:
The real implications of a Lugar loss next week will be psychological: How will watching yet another prominent Republican with a solidly conservative record lose in a primary affect the mindset of average Republican member of Congress? Chances are, it will make him or her even more resistant to taking any action, big or small, that might possibly be construed as ideologically disloyal.
Should Lugar lose, Nate Silver expects a close general election race for the senate seat. Big picture:
Although Democrats still face considerable difficulty in retaining the Senate, their offensive prospects have gradually become more promising over the course of the cycle, with clear pickup opportunities in Massachusetts and Nevada and some prospects in Arizona. Democrats might also hope to have a de facto pickup in Maine, where the independent Angus King is the clear favorite and they have essentially conceded the race to him, although Mr. King has yet to commit to caucusing with either party should he win.