MICHAEL BARONE: Oil spill tars Dems’ reputation for competence. “Obama’s press conference — his first in the White House in 309 days — did not make him look any more in command of things than the photos of Bush’s flyover visit to New Orleans. The candidate who told us his electoral victory would be seen as ‘the moment when the rise of the oceans began to slow and our planet began to heal’ is now the president who seems helpless to prevent the oil slick from spreading. . . . Before the oil spill, the Obama Democrats, noting their policies’ unpopularity, might have asked voters to decide on ‘competence, not ideology,’ as Democratic nominee Michael Dukakis did in 1988. Now, suddenly, that doesn’t seem like a viable theme for 2010 or 2012.”