With the Republican presidential nomination within reach, John McCain is reshaping his campaign to press on without public financing that could limit his spring spending, senior advisers say. The Arizona senator’s rejection of the presidential public financing program he once defended is just the latest evidence of how ineffective the post-Watergate reform has become in an era of multimillion-dollar candidacies. Under the public financing program, McCain could spend only about $54 million on all the primaries and caucuses — a sum Democrats Barack Obama and Hillary Rodham Clinton had spent before the first voters caucused in Iowa on Jan. 3....