This is the most unmet of Obama's campaign promises and the most potentially damaging for his ability to succeed going forward. Once the new President cast his lot with his party in passing an economic-stimulus measure rather than seeking bipartisan agreement, rival Republicans started digging in. The White House's original plan was to leverage Obama's popularity and the agenda-setting power of the majority to force centrist Republicans to break ranks and cast cross-aisle votes on key measures — but the Administration underestimated the weakness of the opposition, which paradoxically strengthened the hand of the conservative activist grass roots, making compromise by GOP officials with the Democrats seem politically untenable. Obama's aides continue to blame the Republicans for refusing to play ball, but the buck stops with the President, whose paths to success on issues such as climate control, jobs and education are all narrower because of a partisan bitterness that rivals that of the Clinton and Bush eras.