Democrats have hit heavy turbulence as they enter a crucial period, with the heart of their agenda in the balance.

The first week after the Memorial Day recess saw a major split emerge between conservative and liberal Democrats over health care, a war supplemental spending bill punted for another week amid internecine sniping, and Speaker Nancy Pelosi (D-Calif.) cracking her whip to get reluctant committee chairmen to act swiftly on the climate change bill.

The Democrats also scrambled to finally react to the investigation of the defunct lobbying firm PMA Group after federal investigators subpoenaed records from the offices of Rep. Peter Visclosky (D-Ind.). Visclosky relinquished his role as an appropriations cardinal, his chief of staff resigned and Democrats called on the ethics committee to disclose whether it is investigating PMA’s ties to Members.

But the canyon-sized split over health care could prove the toughest issue for Democratic leaders in the weeks ahead.

Members of the Progressive Caucus on Friday issued health care reform principles directly at odds with those released by the fiscally conservative Blue Dog Democrats the day before, and the split holds the potential to derail the party’s top priority, just as it did 16 years ago.

Blue Dogs are insisting that any health reform omit a public health insurance plan except as a possible fallback option that would be “triggered— if a reformed private insurance market fails to control costs and improve access to health care.

But the Progressive Caucus is demanding that a public health plan be included from the start, without conditions.

“We oppose any conditions or triggers undermining and limiting the availability of the public option,— the caucus said in a statement.

House Energy and Commerce Chairman Henry Waxman (Calif.) and other top Democrats writing the health care bill strongly oppose the “trigger— idea, arguing it will simply prevent a public plan from ever being put in place.

But Rep. Mike Ross (Ark.), the chairman of the Blue Dogs’ health task force, said the “trigger— approach for a public option has worked to keep insurance companies in check under Medicare Part D.

“Why don’t we simply tell the insurance companies what kind of reform we want and have a trigger for a public option if they don’t do the things we want them to do?— he asked.

Liberals would rather have single-payer, government-run health care to begin with, Ross said.

“They see that as the foot-in-the-door approach to nationalized health care,— he said of the public option.

“We’re not trying to throw up roadblocks for our leadership. We’re trying to be constructive,— Ross continued. “We’re trying to inform them of some of the things we need to vote for this because we want to vote for it, and you know, we have 51 members.—

Ross said he’s also troubled by some proposals that would provide health care subsidies to families of four earning up to $88,000 a year. “The governor of Arkansas will qualify for a government subsidy under what they are proposing,— Ross said. “We’ve got to develop and pass a package we can afford.—

Ross said that he understood other Democrats may grow frustrated at the Blue Dogs but that it’s about simple math.

“When the Democrats start losing seats, it’s going to be the Blue Dogs who are going to lose them first. … If you do the math, you take our 51 Members and we’re back in the minority,— he said.

But health care is just one of the battles in Congress that Democrats are finding difficult to manage.

Democratic leaders are also still scrambling to find the votes for the $90 billion-plus war supplemental after Republican leaders vowed to whip their Members to defeat it because of the inclusion of a $108 billion loan to the International Monetary Fund.

If no Republican votes for the bill, Democrats would need to flip 18 of 51 anti-war Democrats to pass it. But finding those votes is complicated by disputes with the White House over language restricting the president’s ability to transfer detainees from Guantánamo Bay, Cuba, to the U.S. and Senate language that would provide President Barack Obama with explicit legal authority to block the release of detainee abuse photos.

Democratic aides said the disputes were relatively minor and probably could have been cleared up if timing was urgent, or if Obama wasn’t jetting to the Middle East with his team focused on his entreaties to the Muslim world.

“The military isn’t running out of money. There’s no pressure to get it done, and when there is no pressure to get it done, people take their time,— a Democratic aide said.

The third major agenda item — energy — saw Pelosi beginning to crack the whip against chairmen who had been threatening to delay or kill the measure.

House Ways and Means Chairman Charlie Rangel (D-N.Y.) went from saying he would put a cap-and-trade bill on the back burner to saying he would comply with a deadline by Pelosi that his panel finish work on the bill by June 19. Pelosi later called that deadline a goal and said it could be extended if committees needed more time.

House Agriculture Chairman Collin Peterson (D-Minn.) also pulled back a bit from his threats to kill the bill, instead entering intense negotiations with Waxman over protections for the ethanol industry and rural areas.

Pelosi spokesman Nadeam Elshami said the back-and-forth is part of the legislative process. “On health care, on energy, at the end of the day, we will deliver for the American people,— he said.