Warren Buffett called his purchase of the railroad operator Burlington Northern Sante Fe an “all-in wager on the economic future of the United States,” but analysts at Standard & Poor’s don’t appear to share his optimism. The agency on Wednesday placed Buffett’s Berkshire Hathaway Inc. and its affiliates, including Berkshire Hathaway Assurance Corp., on negative watch.

“We believe that this transaction will decrease the liquidity and capital adequacy of the insurance operations,” Standard & Poor’s analysts said in a research update on Wednesday. “For the consolidated organization, financial leverage will increase and fixed-charge coverage may decline.”

The decision means that Berkshire’s municipal securities insurance arm may lose its AAA rating after a fuller credit assessment is complete. A rating downgrade would harm its ability to insure lower-rated municipal debt.

“We are still reviewing the credit and potentially in the next three months we will have resolved the watch,” said Damien Magarelli, a secondary credit analyst at Standard & Poor’s. “It could be sooner, but within the next 90 days for sure.”

The agency issued the release “to give the market an idea of where we’re heading,” Magarelli added. In the report, analysts said “any ratings change would be no more than two notches.”

Market reaction to the release seemed benign. One trader commented that Berkshire is sounder than its competitors and that they have not insured much that is questionable.

Indeed, Berkshire has not insured any municipal securities — at least in the primary market, where Thomson Reuters data is available — since mid-April.

Shares in Berkshire closed at 101,530.00, up 1.08% on the day.

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