A tumultuous first day for the Legislature ended the same way it began: With Democrats clinging to a tenuous one-seat advantage and maintaining – just barely – majority-party status.

On Dec. 30, former Democratic Rep. Barbara Merrill of Appleton left the party, creating a 73-73 tie, with four independents and one Green. Merrill’s move appears a precursor to an independent bid for governor.

Speaker of the House John Richardson faced a tough choice when he learned of Merrill’s move Tuesday, on the eve of the Legislature’s first day back in Augusta. He developed a power-sharing plan that would have split chairmanships of 17 House committees, giving eight to Democrats, eight to Republicans and one to an independent. He was also prepared to offer staff parity to Republicans.

As the Richardson took to the floor to announce his offer, Rep. Joanne Twomey of Biddeford threw on the brakes. Saying her party had lost focus on Democrat’s ideals, Twomey had left it last year. Her positions often took her to the left of the party’s leadership.

When she learned of Merrill’s defection, Twomey re-enrolled as a Democrat, preserving the status quo after a day of chaotic wrangling and hand-wringing. Richardson then decided to leave things as they stood and withdrew his plan to share power with Republicans.

No doubt, the reversal left Republicans disappointed. They were within a few moments of gaining new power within the House. Leaders reacted with a word of caution: With the future uncertain, Democrats should make good on the power sharing or expect similar treatment if electoral fortunes reverse.

Richardson, nonetheless, should be commended for how he reacted first to Merrill and then to Twomey. It took a lot of moxie to embrace a plan that would cast members of his own party out of committee chairmanships. And it was not without risk that he dropped the plan once the numbers reverted to Democrats’ favor.

For her part, Twomey said she never intended to cost any of her Democratic colleagues their committee leadership roles and that she felt her constituents would not approve of the reversal. On the second point, she’s probably right.

Twomey’s erratic behavior and Merrill’s opportunism demonstrate how quickly one party’s fortune can change in a House so closely divided. Overtures of bipartisanship aside, both Republicans and Democrats will face increasing pressure to hold to the party line on controversial issues that wait ahead.

Minority Leader David Bowles and Richardson, so far, have shown themselves adept at holding together their caucuses. As individual legislators feel the pressure of November’s election, mavericks seeking to distance themselves from party orthodoxy will be tougher to control, and electoral self-preservation could trump party loyalty. Controlling the urge to grandstand and score political points will become more difficult. And the temptation to allow every issue to settle into the familiar battle lines we’ve already seen on the budget and Dirigo Health will be enormous.

Session success for the people of Maine depends on healthy debate and a willingness to compromise; otherwise the near-stalemate could leave meaningful legislation stillborn. But with majority status within reach for Republicans and Democrats so close to losing power, it will be hard to hold in check the politics of division.