Barack Obama threatens to withdraw support from wavering Democrats

Barack Obama has said he will not campaign for any Democratic congressmen who fails to support health care reform.

The president will refuse to make fund-raising visits during November elections to any district whose representative has not backed the bill.

A one-night presidential appearance can bring in hundreds of thousands of dollars in funds which would otherwise take months to accumulate through cold-calling by campaign volunteers.

Mr Obama's threat came as the year-long debate over his signature domestic policy entered its final week.

Mr Obama is personally telephoning congressmen who are still on the fence this week, in between several personal appearances devoted toward swinging public opinion.

Yesterday he visited Strongsville, Ohio, home of cancer patient Natoma Canfield, who wrote to the president she gave up her health insurance after it rose to $8,500 (£5,600) a year. Mr Obama repeatedly has cited the letter he received from the self-employed cleaning worker to illustrate the urgency of reform.

Though Congress has already ignored several deadlines set by the president, March 21 is being treated by all sides the final target date, at which time all options would have been exhausted. The president has postponed an overseas trip by three days to see reform through.

Apart from arm-twisting by the White House, an advertising blitz that could cost £20 million by the end of the week, about the same level of a presidential campaign, has been aimed at about 40 undecided Democrats in the House of Representatives.

Most are conservatives who are worried that their support would cost them their seat in November, as the bill has become unpopular with a majority of Americans.

Others are anti-abortion advocates concerned that the proposals would not do enough to prevent government funding of abortions.

The US Chamber of Commerce has led a coalition of organisations opposed to reform, while pharmaceutical companies and Left-wing groups have joined forces to support reform and are urging constituents to contact their representatives and let them know their feelings.

David Axelrod, a senior adviser to the president, said that "the lobbyists for the insurance industry have landed on Capitol Hill like locusts, and they are going to be doing everything they can in the next week to try and muscle people into voting".

The bill would extend health coverage to about 30 million uninsured Americans and would bar insurance companies from refusing coverage to people with pre-existing health problems.

The plan to get it through Congress is so complicated that even experts on legislative process disagree about how it could proceed exactly.

The most likely path to reform is that the House Democrats would pass a Senate version of reform passed on Christmas Eve.

Mr Obama would sign the bill into law before leaving for Asia on March 21, and then both chambers would pass "fixes" to the legislation demanded by the House Democrats.

The rest would, as things stand, be something of a formality. By a process known as "reconciliation," Democrats would frustrate Republican filibuster obstruction tactics in the Senate and allow the health care overhaul to be finalised before Congress takes a two-week break on March 26.

The Democrats have been forced to unorthodox tactics after losing their filibuster-proof majority of 60 in the Senate in a Massachusetts by-election.