Last week, we noticed that of the 64 House Democrats who voted for the anti-abortion Stupak Amendment, only 12 remain. And of those 12, only three (Cuellar, Lipinski, and Peterson) voted for a similar anti-abortion measure last month (both measures effectively excluded abortion coverage from ACA insurance plans). That's a 95 percent reduction in anti-abortion votes from House Democrats in five years.

What happened? Take a look at the chart above. Fully half of the Democrats who voted for the Stupak Amendment lost a subsequent election. In the typical case, where they lost to a Republican, their conservative votes in the House were insufficent to protect them in their conservative districts. A handful lost to a Democrat, in either the primary or general election. Eighteen more Democrats retired (some to run for higher office), one resigned, and one died in office.

So the major reason why there's been such a rapid reduction in the number of anti-abortion votes from House Democrats is they've been replaced by Republicans.

But even if we just look at the twelve Democrats who were there in both 2009 and 2015, 75 percent of them changed how they voted. These nine Democrats are shown in blue above, and deserve some credit for their votes last month. All of them are from districts that President Obama won with more than 55 percent of the vote in 2012.

We found only one statement on the 2015 vote among these nine Democrats, from Mike Doyle of Pennsylvania, who was Bart Stupak's roommate in 2009 and helped facilitate a resolution to the whole Stupak Amendment mess. The statement makes clear he still opposes abortion, but believes this bill "would limit how Americans spend their OWN money and deny American women access to a full range of health care services."

And at least two of these Democrats have signalled a change in their views on abortion in general since 2009. There's the op-ed last week by Ohio's Tim Ryan, describing how his mind was changed on the topic of abortion. And there's also an article documenting a shift in rhetoric on the part of Stephen Lynch of Massachusetts.

No matter the reason, it's clear that the House Democratic caucus has changed significantly since 2009.