This week, Congress returns with House leaders vowing to revisit the anti-abortion bill they pulled off the floor last week. The ban on abortions after 20 weeks was withdrawn when it appeared there weren't enough Republican votes to pass it.

Why did it need quite so many Republican votes? Because the GOP can no longer count on a contingent of Democrats to help out on abortion-related votes.

That was obvious last week, on Thursday, when the leaders brought out a backup bill relating to federal funding for abortion (which is already illegal). It was the 42nd anniversary of the abortion-permitting Roe v. Wadedecision, and it looked bad not to mark the occasion.

The backup bill did pass, but it had to do so with only three Democrats supporting it out of the current 188 in the House. And that speaks volumes about how the House has changed since President Obama was inaugurated.

When Obama took office, there were scores of Democrats in Congress who were anti-abortion and who regularly voted with the Republicans on abortion-related matters — especially abortion funding.

The most visible example in recent years came on Nov. 7, 2009, during floor consideration of the bill that would become the Patient Protection and Affordable Care Act of 2010 (better known as Obamacare).

The Democrats' anti-abortion faction then was led by Michigan Rep. Bart Stupak. After weeks of negotiating with House leaders and the White House, Stupak still insisted on a separate roll call vote regarding the impact the bill would have on abortion. He wanted it to be explicit that nothing in the new law would pay for abortions or pay for health insurance plans that covered abortions.

It was a sticky issue, and if not resolved it threatened to deny the House leaders and the Obama administration the health care law that was within their grasp.

When Stupak's amendment came to the floor, every one of the 176 Republicans in the chamber voted for it. But that would not have been enough to adopt the amendment. The amendment only prevailed because 64 Democrats voted for it, almost exactly one-quarter of what was then Speaker Nancy Pelosi's majority.

Of those 64 Democrats casting anti-abortion votes that day, only 12 remain in the House today.

Obviously, much has changed in the past five years and three months. And the thinning of the ranks of anti-abortion Democrats is even more dramatic than the overall dwindling of the Democratic caucus from 258 seats to just 188.

The winnowing began early. In the month after the vote on the Stupak amendment, Democratic Rep. Parker Griffith of Alabama switched parties. The following year he would lose in his new party's primary to Republican Mo Brooks.

Five other pro-Stupak Democrats lost in primaries or in statewide races in 2010. Five more retired voluntarily, including Stupak himself. Veteran John Murtha of Pennsylvania died.

And in November of that year, 23 more anti-abortion Democrats lost to Republicans. While they had represented a fourth of the Democratic caucus, they accounted for nearly half the incumbent defeats in that election.

The losses continued in 2012 and 2014, when the GOP victories of 2010 were largely protected by new district maps drawn by new Republican majorities in the state legislatures and governors' mansions.

Another dozen pro-Stupak voters who had survived in 2010 retired or met defeat in primaries or the general election in 2012. Five more went down in 2014.

The 2010 route may have been a protest against the liberal program of the Obama administration and its congressional allies, but it wreaked its havoc primarily among Democrats who had not been the administration's loyalists.

The 64 Democrats who stood with Stupak came from outer suburban and rural districts — about half of them in Southern or border states. All but two of the 64 were men; all but a handful were Anglos. In the current House, white males make up less than half the Democratic caucus.

Most of Stupak's supporters were members of the Blue Dog Coalition, a group of Democrats who considered themselves to the right of their party on fiscal issues (and often others as well).

At one time, there had been more than 80 Blue Dogs in the House. In 2009, there were still more than 50 members of the formal group. But 26 were defeated in the fall of 2010 and half a dozen others did not seek re-election. In the current House, they number just 14 (six of whom are also surviving members of the Stupak coalition from 2009).

The great irony here is that the predominantly white, male and moderate-leaning members who voted with Stupak in 2009 felt they were doing it for their districts. Whatever their personal feelings on abortion or its funding by taxpayer money, they knew their districts were against it.

But their vote on this issue, and others, was not enough to dissociate them from their party when the day of reckoning came with a vengeance in 2010. And that election's results are still resonating today.

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