Joseph Lieberman's nomination as Al Gore's running mate in 2000 made him the first Jew to run on a US presidential ticket.

Since then, the 60-year-old senator for Connecticut has left no-one in any doubt that he has presidential ambitions of his own.

I am thinking about the possibility of running for president

Joseph Lieberman

Mr Lieberman has used his position as chairman of the powerful Senate Governmental Affairs Committee to launch high profile attacks on the Bush administration.

He was at the forefront of the decision in May 2002 to issue a congressional subpoena seeking information about contacts between White House staff and the failed energy giant Enron.

In the same month, he joined forces with Republican senator John McCain to demand an independent inquiry into intelligence failures in the run-up to the 11 September suicide attacks.

Lieberman sometimes joins forces with McCain

The two men accused the White House of deliberately sabotaging their efforts, suggesting that the administration was afraid a commission of inquiry might turn up embarrassing government mistakes.

Joining forces with Mr McCain again, the Connecticut senator has also campaigned for stronger measures to combat global warming.

Homeland security

In separate initiatives, he called for the repeal of some of the Bush administration's most expensive tax cuts and pushed for a new national broadband policy to improve internet access.

Before one decides to run for the presidency ...there's an important unofficial primary - the ideas and values primary

Joseph Lieberman

He also co-authored legislation that he says formed the basis of the president's new Department of Homeland Security, designed to protect the American people from attack.

He then sponsored a Senate bill that aimed to deny Mr Bush the power to limit the rights of the department's 170,000-strong workforce - prompting a sharp rebuke from the president.

None of this has done anything to damage Mr Lieberman's reputation as one of Congress's most influential members.

In the Senate, he has served as a member of the Armed Services Committee, the Environment and Public Works Committee, the Small Business Committee, as well as the Governmental Affairs Committee.

Lieberman will not stand against his former running mate

On foreign affairs, he is a strong supporter of Israel and favours normal trading rights with China.

He rallied support in Congress to stop the genocide in Bosnia Hercegovina and Kosovo, and more recently backed a resolution authorising President Bush to use force against Iraq.

Mr Lieberman was born in Stamford, Connecticut on 24 February, 1942, and attended Yale College and Law School.

A Democratic centrist, he has been senator for Connecticut since 1988, and spent the five years before that as the state's attorney-general.

During that time, he built a reputation as a liberal reformer and consumer champion.

More recently, he has styled himself as a moral crusader, featuring prominently in a campaign to name and shame producers of sexually explicit and violent films and other media.

Mr Lieberman's critics attack him for his relatively liberal stance on abortion rights and gun control.

But colleagues say he is more conservative when it comes to issues such as defence spending and family values.

Sabbatarian

The fact that Mr Lieberman is an Orthodox Jew has attracted particular interest.

Both he and his wife, Hadassah, observe the Jewish Sabbath, ostensibly prohibiting him from working from dusk on Friday until dusk on Saturday.

Lieberman: First Jewish vice-presidential candidate

He has said he will vote on legislation and participate in important meetings during that time - but will not campaign, unless it is to promote "the respect and protection of human life and well-being".

Whether Mr Lieberman will campaign for the White House remains an open question.

It depends in part on whether Al Gore decides to stand for a second time, since Mr Lieberman has vowed not to run against him.

But, should the former vice president drop out of the running, Mr Lieberman will have prepared his ground.

"Before one decides to run for the presidency and enter the New Hampshire primary, there's an important unofficial primary - the ideas and values primary," he told one interviewer.

That is one contest the senator for Connecticut would very much like to win.