Mr. Obama’s association with Mr. Ayers, or his decision to continue to attend services at his church, or his remark about bitter working-class voters, are isolated episodes that may say little about Mr. Obama and may pale in significance compared to the weightier issues facing the country. Even so, they are the kind of things that Republicans will no doubt try to use against Mr. Obama. In particular, Republicans are likely to aim that material at blue-collar voters who, to date, have been slow to support Mr. Obama and for whom, Republicans believe, the same questions that Mr. Obama’s critics described as trivial could have great resonance if Mr. Obama is the Democratic candidate in the fall election.