EDM contributor Alan Abramowitz has a must-read op-ed in the Sunday WaPo, “What’s Behind Those Poll Numbers?” Abramowitz argues that Bush’s tanking approval numbers can be attributed to “a growing perception that he simply isn’t competent.” Abramowitz argues further that,

Competence is not a partisan issue. Last week’s polls found that somewhere between 34 and 40 percent of Americans approved of Bush’s job performance. That is discouraging enough. But for Bush and his political advisers what may be more disturbing is the fact that his approval rating among Republicans had fallen to 72 percent, 10 to 15 percentage points lower than the president’s previous level of support from his party’s voters. It’s a sign that even supporters are beginning to question Bush’s effectiveness.

Abramowitz cites the Administration’s history of bungled crises-management, including the Harriet Miers disaster and other examples of poor leadership, especially the Ports deal, which he sees as a major turn for the worse:

While escalating violence in Iraq, the Abu Ghraib prison scandal, the investigation into the outing of CIA agent Valerie Plame and Hurricane Katrina damaged the president’s standing among Democrats and independents, his support from his fellow Republicans remained largely intact — until the ports deal was announced.
…, the takeover is just plain unpopular — with Republicans and independents as well as Democrats. According to last week’s CBS News poll, 58 percent of Republicans along with 71 percent of independents and 78 percent of Democrats oppose the takeover.
Even more significantly, the way the port takeover was handled reinforced a growing impression among the public that nobody is really in charge in the Bush White House. How could the president not even have been consulted on an issue directly involving national security, Bush’s strong suit in the minds of most Americans and especially most Republicans?

Abramowitz believes Bush’s image of incompetence could be contagious for GOP congressional candidates in the November elections:

Unlike the president, congressional Republicans have to face the voters this November. Even though most represent safe Republican districts, only six Senate seats and 16 House seats would have to change hands to give Democrats control of Congress, and there is growing concern among Republicans that they could lose their grip on both chambers if the midterm election turns into a referendum on a president with approval ratings in the thirties or worse.

Abramowitz makes a compelling case that competence could be the pivotal issue in upcoming elections, and his article is highly recommended to Democratic strategists at all levels.