Pakistan's ruling coalition collapsed Aug. 25, torn apart by internal bickering exactly one week after the two main parties united to drive U.S. ally Pervez Musharraf from the presidency.

The exit of the second-largest party is not expected to bring down the government, however.

If anything it clears the way for the main ruling party of slain former Prime Minister Benazir Bhutto to tighten its grip on power and — many hope — to start focusing on challenges such as the sinking economy and the rising militant threat.

The United States and other Western nations have been carefully watching the alliance between Pakistan's two main political parties unravel since Musharraf — a stalwart supporter of the war on terror — resigned to avoid the humiliation of impeachment. Western diplomats say they are worried about the effect prolonged instability could have on the nuclear-armed nation.

Former Prime Minister Nawaz Sharif's announcement Aug. 25 that his party was leaving the ruling coalition, made up of traditional rivals who joined forces to push Musharraf from power, was widely expected.

He had been threatening to walk for days, saying Bhutto's Pakistan People's Party, which has the largest bloc in Parliament, broke repeated promises to restore judges ousted by Musharraf or to agree on a neutral successor.

Sharif vowed, however, to play a "constructive" role while in the opposition.

"We don't want to be instrumental in overthrowing any government," he said at a rowdy, packed news conference.