President Obama is just a sliver ahead of Mitt Romney, his assumed challenger, in a Wall Street Journal/NBC News poll released Tuesday night. The poll puts President Obama at 47 percent, just four points ahead of Romney, at 43 percent. “Obama’s chances for reelection ... are no better than 50-50,” said Democratic pollster Peter D. Hart, who helped conduct the poll. The same poll had Obama with a 49 percent to 43 percent last month, and respondents’ lack of confidence in the economy seem to give Romney a chance to move up further. Just 33 percent of those polled think the economy will get better in the next year, compared with 40 percent who thought that in April.