WASHINGTON | The co-chairmen of President Barack Obama’s deficit commission are sticking with politically explosive proposals to raise the Social Security retirement age and curb benefit increases in a revised plan to wrestle the deficit under control. The new plan by chairmen Erskine Bowles and Alan Simpson, to be publicly unveiled today, faces an uphill slog because of proposals to curb Social Security and Medicare costs, curtail a huge assortment of tax breaks such as the deduction for mortgage interest, and almost double the tax on a gallon of gasoline.