From top White House operative Karl Rove to two of the party campaign committees, Republicans have launched a full-scale attack on MoveOn.org, questioning the liberal group’s patriotism and worldview.

These attacks appear to have two purposes: One is to put the group and its Democratic allies on the defensive over support for the war on terror. And the second is to drive a wedge between Democratic candidates and the millions of dollars that MoveOn’s supporters have pumped into their campaigns.

With MoveOn fast becoming one of the Democratic Party’s most important fundraising sources, the second goal may end up being the more important one.

The 2006 Pennsylvania Senate race provides a window into the developing battle over MoveOn.org.

State Treasurer Bob Casey Jr. (D) was featured recently in a MoveOn e-mail designed to drive donors to support his challenge to Sen. Rick Santorum (R). Within the first 24 hours, the appeal brought in $150,000 for the Casey campaign.

But the National Republican Senatorial Committee immediately went on the offensive with a release titled, “Casey Moves In With MoveOn,” alleging that the group’s e-mail on behalf of Casey shows how closely he is aligned with the “ultra-liberal left.”

John Brabender, Santorum’s media consultant, predicted that if Casey continues to accept MoveOn money, he will have to answer for the group’s controversial policies, which include opposing military intervention in Afghanistan.

“You can tell a lot about a person by the company they keep,” Brabender said. A group like MoveOn “will have a lot of trouble in Pennsylvania, particularly in the middle part of the state. The group will be hung around Bobby Casey’s neck.”

The rhetoric from Brabender and the NRSC is aimed at forcing Casey into a no-win choice: He could pass up a generous source of campaign cash, or he could accept MoveOn’s ample resources, yet face an assault over the group’s issue stances.

Refusing MoveOn money is no small financial decision. In less than 48 hours, the group raised $800,000 for the re-election campaign of West Virginia Sen. Robert Byrd (D) — almost single-handedly quieting rumors that the octogenarian would retire his seat in 2006.

Eli Pariser, executive director of the MoveOn.org political action committee, called the Republican tactics “smart.”

“This is a very pure, very stable source of funds,” said Pariser about his organization. “It is totally unlike the rubber chicken model of fundraising.”

Leading Senate Democrats agree. “They are trying to discredit and smear MoveOn because it’s so successful,” said Minority Whip Dick Durbin (D-Ill.), who added that the group is “one of our most important” fundraising avenues.

Democratic Senatorial Campaign Committee Chairman Charles Schumer (N.Y.) said MoveOn has grown to be so important because the group, through the use of e-mails, has turned grass-roots fundraising upside down.

Long a bastion of conservatives, direct mail used to be the most costly form of fundraising, barely yielding $1 raised for every $1 spent but generally bringing in lots of cash and spreading a sharply worded, partisan message in the missives.

But the costs of MoveOn’s e-mails are negligible, and their haul is often astounding, as Byrd discovered at the end of March.

“Now MoveOn and others have caught up to [conservative direct mailers] and surpassed them, and they’re not happy about it,” Schumer said.

The campaign against MoveOn moved to a new level with Rove’s June 22 speech in midtown Manhattan, not far from the site of the World Trade Center attacks.

Rove accused MoveOn and other liberals of wanting to “offer therapy and understanding for our attackers.” Democrats pounced on the remarks and demanded an apology from Rove, noting that Durbin just the previous day had apologized for likening treatment of prisoners at Guantanamo Bay to those in Nazi Germany or in Soviet gulags.

But rather than issuing an emotional apology — as Durbin did — the White House and Republicans went into full attack mode on MoveOn and other liberals, including Democratic National Committee Chairman Howard Dean.

The Republican National Committee issued reams and reams of documentation on the positions of MoveOn and Dean regarding the war in Afghanistan. The White House refused to offer even a hint of an apology. And the NRSC sent out a fundraising e-mail lambasting MoveOn, beginning with: “Karl Rove was right.”

And a few days later, when MoveOn’s pitch went out on Casey’s behalf, the NRSC again pounced on the group and attacked the centrist-leaning candidate for allying himself with a liberal group — a line of attack that the committee has used mercilessly against Byrd ever since the late March fundraising pitch on his behalf.

Rep. Tom Reynolds (N.Y.), chairman of the National Republican Congressional Committee, said he did not necessarily view the attacks on MoveOn as part of a party-wide effort to drain Democratic funding sources. But, he agreed that it has become a major financial engine for Democrats.

“They certainly have more money there than Howard Dean and the DNC,” Reynolds said, adding, “Many of their investors stand for extremist views.”

For a campaign expected to cost in the neighborhood of $20 million, Casey may not be in a position to reject MoveOn’s dollars even if doing so would save him some political heartburn.

Jay Reiff, campaign manager for Casey, dismissed the idea that his candidate would face any sort of choice.

“Bob Casey’s positions are not going to change based on who happens to endorse him,” said Reiff. “They endorsed him, he didn’t endorse them.”

In their attacks, Republicans are treading a familiar path.

For decades, Democratic candidates have come under fire from Republicans for accepting campaign contributions from trial lawyers and labor unions.

The GOP has also targeted both camps legislatively, including curbs on class-action lawsuits and attempts to prevent unions from using compelled dues for political purposes. Both would effectively limit the ability of trial lawyers and unions to aid Democratic causes.

While such arguments have at times caused Democratic candidates some problems, they have rarely if ever driven them to not accept donations from these interest groups. (Democrats have also attacked Republicans for taking money from social conservatives, big corporations and gun-rights groups, but that tactic has not usually been as central to the party’s campaign strategy.)

Matt Keelen, a former Republican fundraising consultant who’s now a lobbyist with Valis and Associates, insists that MoveOn is a special case.

“It is going to take some time, but MoveOn is making it so easy with their radical, anti-American stances that, over time, people are going to view them as the fringe — to the left of Howard Dean,” said Keelen.

Not so, say Durbin and other Democrats.

“The more they attack them, the more popular they are,” Durbin said of MoveOn.

The GOP’s ability to delegitimize MoveOn, to some degree, hinges on how the war in Iraq plays out. In recent weeks, support for the war has been sinking.

Rep. Harold Ford Jr. (D-Tenn.), who’s running for the Senate in a conservative state by positioning himself as a centrist, said he has no problem if MoveOn wants to help him raise cash.

“MoveOn.org hasn’t placed one road-side bomb in Iraq,” Ford said. “Nor did MoveOn.org fail to plan an exit strategy.”

While the group hasn’t yet helped him, Ford said Rove’s attacks on MoveOn smacked of “childish instinct.”

Pariser added that it will be difficult for Republicans to attack a candidate for taking contributions from a group “funded exclusively or largely by grass-roots people in $25 amounts.”

He points out that recent issues MoveOn has highlighted — opposition to Social Security reform and support of an overhaul of the campaign finance system — are in tune with a large portion of the citizenry.

“There is no position that the organization as a whole has taken that is outside of the mainstream,” said Pariser. “None of those things are something that a candidate needs to fear.”