The US constitution gives Congress significant powers over purse-strings, and Republicans have said they will seek to slash funding for implementation or to chip away at the package in other ways, possibly by attaching provisions to crucial bills like the federal budget.

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Bob Brodersen of the University of California, in Berkeley, has calculated that moving an application from a general-purpose software implementation to a specialised chip can improve efficiency by a factor of 10, 000 (the efficiency metric being millions of calculations per milliwatt of power consumed).

ECONOMIST: MONITOR

The chip card "ultimately makes sense for the United States, but rushing its implementation would be a mistake, " Mr. Ditzion said.

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