Republican Senate leader Mitch McConnell has offered what he calls a “last-choice” option in the impasse over raising the federal debt limit. McConnell’s proposal would require President Obama to seek congressional approval for increasing the debt ceiling by up to $2.5 trillion in three installments. For each request, Obama would have to propose an equal amount in spending cuts to balance out the funds he would be seeking. Administration officials and Democratic leaders say they will review McConnell’s plan. But the proposal faces its toughest challenge in the House, where Republicans say they will not approve any plan that does not impose massive spending cuts.