Chris Maddaloni/Roll Call/Getty Images

By our count - and the day is still young - four Democratic U.S. senators have flipped on gay marriage in the past few days. Senators Jay Rockefeller, D-W.Va., and Mark Begich, D-Alaska - have joined Senators Claire McCaskill, D-Mo., and Mark Warner, D-Va., in renouncing their previous opposition to gay marriage, just since Sunday.

They follow, of course, Hillary Rodham Clinton and Sen. Rob Portman, R-Ohio - still the only Republican senator to endorse gay marriage - to flip as the Supreme Court takes up the issue today and tomorrow.

We've talked extensively in recent days about politicians following the public on this, with support now up to 58 percent for gay marriage in our latest ABC News/Washington Post poll.

Still, this is a stunning exodus of lawmakers who've been in public office for decades, and who represent red and purple states. There has rarely been such a swift move on a social issue in such a short period of time - a mark of how the debate has shifted, and has even been flipped on its head.

Not long ago, it was opponents of gay marriage bringing gay marriage up as a wedge issue. Those voices are remarkably silent now. And it's easy to imagine the wedge cutting in the opposite direction in the not-so-distant future.

It's increasingly hard to picture any Democratic candidate for president opposing gay marriage in 2016, and we heard from Karl Rove on " This Week" that it's easy to picture at least one Republican 2016er supporting gay marriage.

Update at 3:10 p.m.

ABC's Z. Byron Wolf adds - Make that five senators who have flipped on gay marriage in the past two days.

Montana Democrat Sen. Jon Tester joined the party too with a Facebook message.

"Montanans believe in the right to make a good life for their families. How they define a family should be their business and their business alone. I'm proud to support marriage equality because no one should be able to tell a Montanan or any American who they can love and who they can marry." -JT

Tester also changed his Facebook profile picture to the pro-gay marriage red logo that has been trending in social media.