Reflecting investor optimism about passage, the cost of insuring exposure to a U.S. debt default dropped on Tuesday, but some concerns remained because of the tight timeline and opposition from some lawmakers. Last week, credit rating agency Fitch placed its "AAA" rating of U.S. sovereign debt on watch for a possible downgrade, citing downside risks including political brinkmanship and a growing debt burden. In a previous debt ceiling crisis in 2011 rating agency Standard & Poor's cut the U.S. top 'AAA' rating by one notch a few days after a debt ceiling deal, citing political polarization and insufficient steps to right the nation's fiscal outlook. "Even if a U.S. default is averted, a ratings downgrade could still happen," Vishwanath Tirupattur, a strategist at Morgan Stanley, said in a research note on Sunday. Some also fear a debt ceiling resolution could only provide short-term relief to markets because the U.S. Treasury is expected to quickly refill its account with bond sales, sucking out hundreds of billions of dollars of cash from the market.

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Persons: Joe Biden, Kevin McCarthy, Fitch, Raymond James, Ed Mills, Alex Anderson, Vishwanath Tirupattur, Morgan Stanley, Spokespeople, Blair Shwedo, Davide Barbuscia, Shankar Ramakrishnan, Pete Schroeder, Megan Davies, David Gregorio Our Organizations: YORK, Democratic, Republican, U.S . Treasury Department, BMO Capital Markets, AAA, Moody's, U.S . Treasury, Thomson Locations: U.S