BOSTON, Jan 20 (Reuters) - In a stunning blow to President Barack Obama, Republican Scott Brown won a bitter U.S. Senate race in Massachusetts on Tuesday and promised to be the deciding vote against his sweeping healthcare overhaul.

Brown's win robbed Democrats of the crucial 60th Senate vote they need to pass the healthcare bill and sent shudders of fear through Democrats facing tough races in November's congressional elections.

What once seemed an easy Democratic victory turned into a desperate scramble in the last few weeks as Brown surged ahead of Democratic state Attorney General Martha Coakley on voter fears over the economy, the healthcare bill and Obama's agenda.

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WASHINGTON (CNN) -- President Obama said Wednesday he was unable to guarantee that health care reform won't change how Americans get medical treatment, but he said any changes would be necessary and positive.
In a nationally televised news conference dominated by the health care issue, Obama delivered lengthy statements in response to Republican attacks on proposals he favors.

He also attempted to ease the concerns of people left confused by the fierce debate in Washington.

He repeatedly emphasized that the spiraling costs of the current system would bankrupt the nation while denying coverage to millions more Americans.

Asked directly if he could guarantee that an overhauled health care system won't change how people receive treatment, Obama said no.

"The whole point of this is to try to encourage what works," Obama said, addressing concerns that reform would take away the ability of people to choose their doctors and treatment. Watch Obama describe importance of "getting it right" »

"The government is already making some of these decisions," Obama said. "Insurance companies are making some of these decisions."

The reform proposals he backs would have experts make decisions based on the best medical treatment, not accountants attempting to save money or doctors prescribing treatments that bring the highest fees, Obama said.

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