Speaker Nancy Pelosi (D-Calif.) has been courting and protecting House Agriculture Chairman Collin Peterson (D-Minn.) for the better part of a decade, but Peterson lately hasn’t been returning the favors.

The Minnesota Democrat has emerged in recent weeks as the most outspoken critic of sweeping climate change legislation that Pelosi views as her legacy project. And his continued opposition would make it difficult, if not outright impossible, for leaders to pass the package before lawmakers leave town for the July Fourth recess.

Peterson has demanded that the Environmental Protection Agency be stripped of its ability to regulate ethanol production and wants to prevent the EPA from having a role regulating carbon offsets under the cap-and-trade proposal.

House Democratic staff worked through the weekend to strike a deal but a breakthrough remained elusive at press time.

Looming large over the measure’s fate is Pelosi’s long history with Peterson, a rare moderate ally. Sources close to both said that while Peterson has been brusque publicly, he is negotiating in good faith behind closed doors — and that Pelosi knows his gripes about the bill speak to real concerns among a critical bloc of moderate and rural Democrats that need to be addressed for the bill to pass.

“You can see him as a big pain in the ass and dragging it out this long, but in the end he’s the guy we need to pass this bill, and she knows that,— said a House Democratic aide. “She cannot move her flagship issue without his input.—

Aides noted that Pelosi courted Peterson and other rural Democrats for years, even flying with Peterson, a pilot, in his small plane and starting a rural working group when Democrats were in the minority. And Pelosi provided key support for Peterson to get the Agriculture ranking membership in 2005, even though he had voted with Republicans on major bills and for years was derelict in his political support for the party.

“Their relationship is extremely close and it has been for a very long time,— said a House leadership aide. And although Peterson has disparaged the cap-and-trade bill repeatedly and threatened to kill it if his demands aren’t met, Energy and Commerce Chairman Henry Waxman (D-Calif.) and senior aides close to the process give him credit for working toward a deal.

Pelosi started cracking her whip shortly after the Energy and Commerce Committee passed the climate change bill in May, with Peterson warning he had the votes to derail it and Ways and Means Chairman Charlie Rangel (D-N.Y.) considering wholesale changes. Pelosi set a June 19 goal for committees to hold markups — none did — and committees will instead get a chance for input via a manager’s amendment this week if Pelosi succeeds in getting the bill to the floor.

Waxman in particular has been angling for quick action since debate over a health care overhaul will likely dominate July. But insiders said Pelosi is taking a more cautious approach to ensure leaders have the votes lined up before the measure hits the floor.

Nevertheless, this week could be the test of whether Pelosi’s long courtship of Peterson will pay off for her signature issue. “This is where he could really deliver on that relationship,— the aide said.

Or not.

Peterson, a member of the Blue Dog Coalition, has been bipolar on the bill, vacillating from outright hostile to luke-cold. At one point, he said that he had as many as 45 votes to kill it on the floor. Following a meeting with Pelosi, he agreed to work toward a compromise with Waxman. Peterson was all over the map last week, saying at various points that progress had been made on his concerns, only to later say that opposition had continued to grow to the bill, and finally on Friday warning that negotiators had to go back to the drawing board after talks blew up the night before.

Peterson’s positioning on the climate legislation comes four and a half years after the Minnesota Democrat secured the top job on the Agriculture panel by promising leaders he would work harder to be a team player.

Back then, his ascension should have been a no-brainer: In a party that rarely breaks from honoring seniority, he ranked next in line behind then-ranking member Charlie Stenholm (D-Texas), who had lost his 2004 re-election bid. But Peterson had earned a reputation for being unreliable, rarely participating in the Caucus, voting against the party on measures like the Medicare Part D prescription drug benefit, and going nearly a decade without paying his dues to the Democratic Congressional Campaign Committee.

Peterson had a key ally in Pelosi, whom he supported early on during her runs for Minority Whip and Leader. But she made clear to him in a private meeting that if he wanted the job, he would have to prove himself a loyal soldier. Peterson responded swiftly, cutting checks worth $70,000 to the DCCC and launching an intense lobbying campaign in the Caucus to reassure colleagues.

With Pelosi’s backing, Peterson got the job. Last year, she went to the mat for Peterson again, pushing through a farm bill that came under criticism from environmentalists and some liberal Members.

Peterson, in turn, has demonstrated that he can open his wallet, contributing more than $400,000 to the party committee over the past two cycles and spreading another $200,000 to Democratic candidates and groups, according to figures from CQ MoneyLine. He paid his dues right off the bat in 2007, chalking it up to a personal nudge from Pelosi. “I’ve been supporting her, and she’s been supporting me on the farm bill,— he said at the time.

And he made a significant early dent in his dues for this Congress, contributing $100,000 back in March toward the $250,000 he owes. Only two other nonexclusive committee chairmen, of 17 at that dues level, contributed as much in the first quarter. Thursday, he headlined a luncheon fundraiser at the DCCC to benefit vulnerable Democrats on his committee.

“He’s absolutely a team player,— said Stenholm, now a lobbyist. “But that doesn’t mean you just arbitrarily do what the Speaker, or any other member of leadership, wants at any time. He has an obligation to his home district, and, as chairman, to the agriculture community, and he’s doing his best to stand up for that.—