Tensions between the presumptive presidential nominees escalated over Sen. Barack Obama's refusal of public funds and Sen. John McCain's call to lift a ban on offshore drilling. Mark Shields and David Brooks discuss the political news of the week.

A provision in the new Senate energy bill would increase fuel economy standards for cars and trucks by 2020. Sens. Dick Durbin, D-Ill., and Kit Bond, R-Mo., debate the measure.