Coming Up on This Week with George Stephanopoulos

— -- In a Sunday exclusive, George goes "On the Trail" with Sen. John McCain, R-Ariz. After sweeping the Republican Potomac primaries and earning the endorsement of former rival Gov. Mitt Romney, R-Mass., McCain is in Wisconsin seeking to solidify the Republican nomination. Can the frontrunner bridge the divide with conservatives? McCain talks about the state of his campaign and looks ahead to the contest with the Democratic nominee.

Then, on our "Roundtable," EJ Dionne, Claire Shipman, Jay Carney and George Will debate the week's politics.