In an appearance on CBS's "Face the Nation," Rubin -- who served in the Clinton administration and now is chairman of Citigroup -- said we live in a "very complex, very uncertain time."
"Could get a little bit worse," he said. "There's always some chance that matters could get better more rapidly, but I think that's a very low probability. And there's some chance, and hopefully ... it's a low probability, that things could get considerably worse."
Rubin advocated being "highly proactive in doing whatever is sensible to address our economic issues." He said he likes Obama's economic proposals, including a middle-class tax cut, a second economic stimulus package and a major effort to develop alternative energies.
Former Hewlett Packard chief Carly Fiorina, an economic adviser to Sen. John McCain, R-Ariz., Obama's likely opponent in the November general election, said on the same program things could get worse but she said Obama plans to raise taxes, expand government and implement isolationist and protectionist policies -- which would help make the economy worse.
She backed McCain's proposed tax cuts, steps to curb the credit crisis and his energy plan. She said he is "focused on accelerating job creation."
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