By Kevin Anderson BBC News Online Washington Correspondent

Democrats have brought the Enron scandal to the White House, issuing the first congressional subpoena of President Bush's term.

The subpoena asks for information about contacts between White House staff and failed energy trader Enron.

It is an election year, and in recent weeks, Democrats have shown a willingness to attack the hugely popular president.

I have finally concluded that we were being slow-walked ... at the least and stonewalled at worst

Senator Joseph Lieberman

Last week, they criticised Republicans for using a photo of Mr Bush on September 11 to raise funds and questioned whether the administration acted vigorously enough on warnings of terrorist threats ahead of the attacks.

These are the opening salvos in an important election that will determine the balance of power in Congress and the extent to which Mr Bush is able to pursue his domestic agenda.

Democrats see an opening

Democrat Senator Joseph Lieberman said of White House's efforts to co-operate with the committee's investigation, "I have finally concluded that we were being slow-walked ... at the least and stonewalled at worst."

Mr Lieberman was Al Gore's running mate in the 2000 presidential election and one potential candidate for the Democrat nomination for president in 2004.

Democrats see a possibility to capitalise on public outrage over the scandalous collapse of Enron.

The company appears to have pushed the limits of creative accounting, and executives grabbed millions as the company sank into bankruptcy whilst employees saw their retirement investments evaporate.

Enron was one of Mr Bush's largest campaign contributors, and former Enron CEO Kenneth Lay was one of Mr Bush's Pioneers, a group of key fundraisers that helped him raise a record-shattering war chest.

And Mr Bush's ties to the energy industry might also be a liability that Democrats could exploit.

Not only Enron - with its shell companies and self-enriching executives - but a host of other energy companies are increasingly looking ethically challenged with revelations that they might have padded their profits with so-called "round-trip" trades and manipulated power markets.

White House defence

The White House has fiercely defended its right to hold confidential consultative meetings.

White House officials, including Vice President Dick Cheney, claim executive privilege in its policy meetings with members of the public and of industry.

This is nothing more than a decision to have a look-see to see if something might possibly turn up

Senator Fred Thompson

The General Accounting Office, the investigative arm of congress, has already issued a subpoena for information about meetings Mr Cheney held with members of the energy industry in crafting its energy policy.

Republicans said Mr Lieberman's moves were politically motivated.

"This is nothing more than a decision to have a look-see to see if something might possibly turn up," Republican Senator Fred Thompson said.

The White House had asked Mr Lieberman not to issue the subpoena until the committee had time to review what the White House was willing to submit for review.

"They have issued a subpoena without even having a chance to review the information that we're sending," said White House spokesman Ari Fleischer.

Dangers for Democrats

But these are the opening manoeuvres in an important mid-term election.

Mr Bush's domestic agenda had stalled before the September 11 attacks after the balance of power tipped to the Democrats in the Senate.

Republicans hope to build on Mr Bush's popularity to retake the Senate and build on their majority in the House of Representatives.

Democrats are looking for a political opening, but they must tread carefully.

The president's approval ratings remain in the stratosphere, and their Republican colleagues, who pilloried Bill Clinton zealously, can attest to the dangers of attacking a popular president.

And Democrats are not without their own links to Enron.

The company was a prolific political contributor, and giving some $5m to federal candidates over the past decade, according to Common Cause, a group that advocates for campaign finance reform.

During that time, 71 senators and 168 members of the House of Representatives reported having taken money from the failed energy giant, Common Cause reports.

While 70% of Enron's contributions went to Republicans, Democrats also benefited from Enron's largesse, which may limit the ability of Democrats to claim they are entirely without the taint of Enron's influence.

But so far, Mr Bush can take comfort that key figures in the administration did not aid Enron when it called in need.

Mr Lay called members of the Bush cabinet including Secretary Paul O'Neill and Commerce Secretary Don Evans as Enron entered its death throes. There is no evidence that either Mr O'Neill or Mr Evans acted to prevent the company's collapse.

And the president is fortunate. In quieter times, the public might pay more attention to the scandalous burnout of Enron, but they are preoccupied with warnings of fresh terror attacks.

But none of this will deter Democrats from looking for a 'smoking gun' to tie Enron's collapse to the administration and whittle away Mr Bush's popularity.