Updated 1:36 p.m.

Although Sen. Judd Gregg (R-N.H.) insists that a Republican must take his place, his pending departure from the Senate will likely still benefit Democrats in the long run.

President Barack Obama is on track to nominate Gregg to be his Commerce secretary today, leaving the Republican’s Senate seat to be held by a caretaker for the final two years of his term — and likely setting up an open race for the seat in 2010.

In a statement from his office Monday evening, Gregg insisted he would not take the Commerce post unless his successor is a Republican. Under New Hampshire law, Democratic Gov. John Lynch has the power to appoint Gregg’s replacement without regard to the appointee’s party.

“I have made it clear to the Senate Leadership on both sides of the aisle and to the Governor that I would not leave the Senate if I felt my departure would cause a change in the makeup of the Senate,” Gregg said. “The Senate Leadership, both Democratic and Republican, and the Governor understand this concern and I appreciate their consideration of this position.”

Lynch has scheduled a 4:30 p.m. press conference today to announce his appointment of Bonnie Newman, Gregg’s former chief of staff, to the Senate seat. Newman, who most recently served as the interim president of the University of New Hampshire, is seen as a Republican placeholder to keep the seat for two years, which would give Democrats a good shot at the open seat in 2010.

Newman supported Lynch’s bid for governor in 2004 — a contest the Democrat narrowly won over a two-year Republican incumbent.

But Newman has never run for any political office, so it’s unclear just how she would work with Senate Republicans.

“She’s not an ideologue,” said former New Hampshire Republican Party Chairman Fergus Cullen, who described Newman as “something of a mentor” to him. “I have no idea where she stands on foreign policy, domestic policy, and I suspect very few people do.”

Cullen said it would be unlikely that Newman would want to stay in the Senate for longer than two years.

“She has steadfastly avoided partisan politics for most of the last several years,” Cullen said. “She has not been a political activist at all.”

What’s more, whomever Lynch picks to fill the Senate vacancy will not have same incumbency advantage as Gregg would have running for re-election. Democrats were already targeting the Senate seat, with two-term Reps. Paul Hodes and Carol Shea-Porter looking at challenging Gregg. National Democrats were even courting Lynch to run against Gregg in 2010, but the Democratic governor announced last month that he was not interested.

Not only have Democrats picked up two House seats and a Senate seat in New Hampshire over the past two election cycles, but the party’s bench in the Granite State continues to be very deep. There is no shortage of Democrats in the state who would be interested in running in an open-seat race for Senate.

“Our chances of picking up the Gregg seat just increased tenfold,” New Hampshire Democratic Party Chairman Ray Buckley said Monday. “With the changing demographics of New Hampshire, this will be a Democratic pickup in 2010. There is simply no doubt about it.”

If there is an open seat, Hodes would be extremely likely to run. Shea-Porter, however, has been coy about her intentions. Her spokeswoman did not respond to a request for comment Monday.

National Democrats are less excited about a potential Shea-Porter Senate bid because her district is more conservative and they do not want to risk losing her House seat while she steps down to run for Senate.

If Hodes or Shea-Porter shy away from a bid, Democrats would likely look to Katrina Swett or her husband, former Rep. Dick Swett, to run for the Senate seat. The former Congressman lost a bid for Senate in 1996 by a small margin.

The daughter of late Rep. Tom Lantos (D-Calif.), Katrina Swett still has almost $1 million in her campaign account. She abandoned her bid for the Senate in 2007 when now-Sen. Jeanne Shaheen (D-N.H.) got into the race and cleared the field.

Democratic sources also point to several female Democratic leaders in the Legislature, such state Senate President Sylvia Larsen, state Senate Majority Leader Maggie Hassan and Speaker Terie Norelli, all of whom would also make formidable candidates in a Senate race.

Assuming Gregg’s replacement gives up the seat in 2010, Republicans would likely look to former Sen. John Sununu (N.H.) as a possible candidate.

Sununu lost re-election to Shaheen in November but departed the Senate as its youngest Member at age 45. A request for comment from Sununu through a spokeswoman was not returned.

Many Granite State political observers thought Gregg might retire in 2010, which is why, according to one Republican operative in the state, Sununu supporters were told to “hang onto your signs.” Sununu’s father, former Gov. John Sununu, is the newly elected Republican Party chairman in the state.

“If Sununu wanted it, it would be his,” said the Republican operative in the Granite State. “I don’t think there would be any significant primary opposition. Should he not decide to get in, I think that opens the door.”

Republicans could look to Manchester Mayor Frank Guinta as a possible candidate. Guinta has so far been more focused on running for governor in 2010 — perhaps challenging Lynch if he decides to run for re-election.

Republicans could also tap Attorney General Kelly Ayotte to run. Former state Health and Human Services Commissioner John Stephen, who lost the 1st district Republican primary in 2008 to former Rep. Jeb Bradley (R), could also be interested in running. Fellow former Rep. Charles Bass (R) might also be interested. Bass and Bradley lost their seats in the Democratic tidal wave of 2006.