There was a political scramble in Maine after Tuesday's surprise retirement announcement from Olympia Snowe, one of the state's two Republican senators.

Robert Siegel talks to three former GOP party chairmen and governors about the results of Tuesday's primaries in Michigan and Arizona. Haley Barbour of Mississippi says the campaign should now focus on social issues. Marc Racicot of Montana agrees, but says attention must be paid to those who care about such issues, and Jim Gilmore of Virginia says he feels a connection must be made between the GOP and blue collar voters.

Former Massachusetts governor Mitt Romney, who narrowly won Michigan's Republican primary on Tuesday, traveled south to campaign in Toledo, Ohio on Wednesday. Ohio holds its primary next week on Super Tuesday.

Romney's campaign was out with a new web video meant to remind Republicans in Ohio, Tennessee, Georgia with primary elections in less than a week that Santorum sough votes from Michigan Democrats. For Romney, it was a chance to gain the upper hand as each man in the struggle to persuade Republican voters that he is the truer conservative and his rival is merely a pretender.

Presidential debates can provide a boost to a candidate, thwart a lead in polls or prompt a decision to leave the race. NPR's Ken Rudin and Alan Schroeder, author of Presidential Debates: 40 Years of High-Risk TV, look at game-changing moments in the 2012 election cycle.