Republican former Secretary of State Colin Powell's endorsement of Sen. Barack Obama is the latest sign that the Republican Party's coalition is fracturing amid the stresses of the campaign.

Appearing on NBC's "Meet The Press" Sunday, Gen. Powell lamented his party's tilt to the right and a campaign by Sen. John McCain that he said had dwelled too much on inconsequential issues and attacks.

Gen. Powell, a secretary of state under George W. Bush, echoed many conservative intellectuals in his criticism of Republican vice-presidential candidate Sarah Palin, saying: "I don't believe she's ready to be president of the United States....That raised some questions as to the judgment that Sen. McCain made."

Some Republicans, including Sen. McCain, dismissed the significance of the endorsement. "It doesn't come as a surprise," the senator from Arizona said in an appearance on Fox News Sunday. "I'm very pleased to have the endorsement of four former secretaries of state, well over 200 retired generals and admirals. I've admired and continue to respect Secretary Powell."

The endorsement comes after a series of events that have pointed to the fraying of a Republican umbrella that has relied in the past on both moderates and conservatives to bulk up its governing majority.