Democratic pundit Bob Beckel has been under contract with Fox News for six years. And in the midst of the White House war against the cable network, some of his liberal friends think that’s six years too many.

They invited him to lunch the other day for an intervention: Why is Beckel — a true-blue Democrat who worked for Robert F. Kennedy and ran Walter Mondale’s 1984 presidential campaign — giving comfort to the enemy?

Beckel’s response: “I talk to more persuadable voters in a month than anybody on MSNBC and CNN talks to in a year.” 

In the eyes of some of their party brethren, Beckel and other Democratic strategists and pundits who appear regularly on Fox News are traitors to the cause. Or at least gluttons for punishment.

And some of them feel that way, too.

“It sucks,” says Democratic direct-mail consultant Liz Chadderdon, a regular on the network. “It is very, very tough to be a Democrat on Fox.”

During an October 2007 hit on “The Factor,” Chadderdon referred to the detainees at Guantanamo Bay as “victims.” It was a verbal faux pas, and she knew it. But no sooner did she get off the air than she received a death threat — the first of a handful she says she’s received after appearing on Bill O’Reilly’s Fox show.

More recently, Chadderdon has been invited to talk business with Fox’s Neil Cavuto — on the main network and on the two-year-old Fox Business Network — even though she readily admits that she has no background in economics.

“Speaking about those issues is not my forte,” said Chadderdon. “And I’m getting the tar kicked out of me.”

So why does she keep doing it? For pretty much the same reason Willie Sutton robbed banks. Fox is where the viewers are — No. 1 in the prime-time news ratings and drawing more than twice as many viewers on weeknights as either MSNBC or CNN.

“You know how I know nobody watches CNBC?” said Chadderdon. “I compared the pope to my 11th-grade algebra teacher, and nobody sent me a letter.”

Lanny Davis, former White House counsel for Bill Clinton, says some of his fellow Democrats privately encourage him to keep appearing on Fox — even as they boycott the network themselves.

“I get very positive but whispered reinforcement,” he said.

Davis made news during last year’s Democratic presidential primaries when he said that Fox was the fairest of the cable networks in its treatment of Hillary Clinton.

And now, he insists, the claims of bias directed at Fox are overstated, at least insofar as they come from devotees of one of its competitors.

“Is there a difference between Fox and MSNBC?” he asked. “You count the number of guests on Rachel [Maddow] and Keith [Olbermann] who are conservative Republicans. If you get to double digits, I’ll buy you dinner for each one.”

Susan Estrich is perhaps the most identifiable Democratic pundit on the network. She’s been on the payroll for more than a decade, having first gotten to know Fox News President Roger Ailes when they were working on opposite sides of the 1988 presidential campaign.