The same activists are now seeking to bend Senator Hillary Clinton to their anti-war side or face defeat in the Democratic presidential primaries. Her supporters are concerned that the “jihadist” left, galvanised by the victory of East Coast millionaire Ned Lamont, are on the rise in the Democratic party, starkly affecting its national electoral prospects.

Mike McCurry, White House press secretary during Bill Clinton’s presidency, said: “The very idea of centrism is under attack now in the party. We have our own loony left too.”

The former first lady, whose strategy for winning the presidency in 2008 has been based on persuading the electorate she is a genuine moderate and tough on national security, is watching her back warily.

“She’s got to read the results with a certain anxiety,” said McCurry, who remains close to the Clintons. “There is a very angry Democratic base out there and it’s perilous for ‘new Democrats’. She is going to be figuring out a way to heavy-up the anti-Bush message.”

Clinton faces a potentially deadly squeeze between Republicans, who are ramping up their charges that the Democrats are soft on terror in the wake of the airliner bombing plot, and her own party activists who have received all the proof they seek that untrammelled opposition to President George W Bush and the war in Iraq is an election winner.

If the New York senator is to win the Democratic nomination for president, she will need the support of her party base in the presidential primaries.

Flush with Lieberman’s defeat, Michael Moore, the left-wing film-maker, warned that the tumbrils would keep rolling. “I’m here to tell you,” Moore warned Clinton, “that you will never make it through the Democratic primaries unless you start strongly opposing the war.”

Clinton quickly shored up her position on the left last week by telephoning Lamont to congratulate him on his victory and dropping $5,000 (£2,650) into his electoral coffers.

“I am going to work for the Democratic nominee,” she said. “And I told him I would do whatever I can and whatever he wants me to do to help him in his election.”

She also declared that “there is a great deal of difference” between her position on Iraq and Lieberman’s. Days before the primary vote, in a nifty use of her influence on the Senate armed services committee, she summoned Donald Rumsfeld, the defence secretary, and then demanded his resignation for mismanaging the war (a position Lieberman has not taken).

Clinton’s deft political manoeuvring prompted Markos Moulitsas, the dailykos.com blogger who is regarded as the left’s kingmaker, to put Clinton in his “winners” column last week. Moulitsas, however, has made no secret of his antipathy. She takes “every position, so she stands for nothing — that’s why ‘netroots’ don’t like Hillary,” he said.

The Connecticut result places Clinton in an ever more delicate spot. Lieberman, the party’s vice-presidential nominee in 2000, intends to stand as independent Democrat in the November Senate elections and Clinton has not asked him to withdraw.

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