Chekhov, the legendary 19th-century Russian dramatist, liked to articulate his rule for creating suspense. He reputedly decreed: "If you say in the first chapter that there is a rifle hanging on the wall, in the second or third chapter it absolutely must go off." Actually, some scholars think the quote was slightly different: "One must not put a loaded rifle on the stage if no one is thinking of firing it."

Either way, the latest flap about abortion is positively Chekhovian.

All through the spring and summer, as Congress debated and negotiated health care reform, the abortion issue has been sitting out there, like a loaded weapon perched in the corner of the stage, creating suspense by its sheer presence, and, in accordance with Chekhov's rule, it was only a matter of time before somebody picked it up and fired. And blew a big hole in the Democrats' reform package, requiring major surgery.

What happened in the House on Saturday night (the passage of a restrictive anti-abortion provision, as the necessary price for securing support from anti-abortion Democrats for the overall reform package), and what may well happen next in the Senate (anti-abortion Democrats insisting that the Senate adopt the same provision, as the price for securing their support on reform) is actually a symptom of the Democratic party's recent electoral achievements. It's quite perverse, really. The Democrats have succeeded so well at crafting an ideologically diverse majority that now this same diversity might imperil the entire health reform effort.

To build and enhance their majorities in the House and Senate, Democrats in 2006 and 2008 recruited socially conservative candidates to run in socially conservative states. The strategy worked. Today, they have a robust crop of rank and filers who adamantly oppose abortion - and now, as the health reform push nears the eleventh hour, they're on a collision course with the much larger cohort of congressional Democrats who want to safeguard abortion rights.

Anti-abortion Democrats vow not to support health reform on final passage unless the restrictive language stays in. Their successful House provision bars abortion coverage in any government-run plan, and makes it exceedingly difficult for lower and middle-class women to get abortion coverage from the private insurance companies that intend to offer health plans in a new federally-supervised marketplace program. Sixty-four Democrats voted for that provision on Saturday night, roughly one-fourth of all House Democrats. That's enough voters to sink any final bill that emerges from a Senate-House conference committee (assuming one does emerge).

Meanwhile, some moderate/conservative Senate Democrats want to adopt that House provision, and vow not to vote Yes on reform itself unless the abortion crackdown language is included; yesterday, Sen. Ben Nelson of Nebraska said yesterday that without such a crackdown, "you can be sure I would vote against it" - and even though it's a tad galling for a guy from Nebraska to essentially dictate the health choices for lower and middle-class women nationwide, that's how the game is played. The Senate Democrats need all 60 of their brethren in order to even force a floor vote.

Yet if the Nelson types do get their way, the abortion-rights congressional Democrats are vowing to sink reform for their own reasons. House liberals reportedly have gathered more than 40 signatures already, declaring that they do not intend to aid and abet what they view as the biggest curb on women's legal abortion rights in a generation.

(Are the pro-choicers overstating the case? You decide. The anti-abortion language, which Nancy Pelosi had to swallow in order to eke out passage of the reform bill, decrees that no taxpayer money can be used for "any part of any health plan." Which means that any modest-income women who purchase private health insurance in the new marketplace program with the help of a federal subsidy would not be allowed to get abortion coverage. And if these companies can't sell abortion coverage in the new marketplace program, they might limit that coverage in general. Which would adversely affect those women who are capable of buying a health plan entirely with their own money.)

One is tempted to challenge these abortion foes who protest the use of any tax dollars, even indirectly. All of us pay taxes that finance or subsidize all sorts of things that we find morally objectionable - the elective war in Iraq and its ruinous legacy come quickly to mind - but at the moment waxing philosphical is a luxury that Democrats can't afford. All that matters now are the vote tallies for final passage.

President Obama, who is generally reluctant to get into the policy weeds, finally weighed in on this issue yesterday, voicing concern that the anti-abortion language will have the effect of "restricting women's insurance choices" - and he ought to be concerned, since the amendment potentially undercuts his recent pledge that "if you're happy and satisfied with the insurance that you have, it's not going to change." But it's doubtful that his concerns will have much impact on however this issue plays out, given the clash opf emotions and convictions. Here in the final act, Chekhov's rifle has been fired and the smoke hangs in the air.