What began as a slow drip has turned into a flood over the last two weeks of Senate Democrats switching long-held positions and now coming out publically to endorse same sex marriage.

The number of Senate Democrats left to endorse marriage equality is so small, that you can count them now on one hand - bringing much pressure from supporters of gay rights for the remaining "holdouts" to quickly change their position.

The question now among Senate Democrats is not who has endorsed gay marriage anymore - but now, who hasn't?

The holdouts among Senate Democrats face public pressure.

The most recently ABC News/Washington Post reveals that support is now up to 58 percent for gay marriage in the most recent up from 32 percent nine years ago.

The momentum of the flood of Senate Democrats switching their views can be attributed mostly to last week's arguments in front of the Supreme Court in which the court heard two cases challenging the constitutionality of gay marriage.

But the shift on such a controversial social issue has come at seemingly lightening speed, each new day it seems brings a new Democratic Senator revealing their change in stance after much contemplation.

Today two Freshman Democratic Senators from conservative states, Sen. Sen. Joe Donnelly, D-Ind., and Sen. Heidi Heitkamp, D- ND., announced their support for gay marriage - a mere months after running - and winning - in their states as opponents of gay marriage.

Intrinsic in both the Senator's statements today was the notion that the public tide had helped to shift their personal stance on the issue.

"In speaking with North Dakotans from every corner of our great state, and much personal reflection, I have concluded the federal government should no longer discriminate against people who want to make lifelong, loving commitments to each other or interfere in personal, private, and intimate relationships," Sen. Heitkamp said today, a nod to the public opinion in her red state changing on the issue.

In announcing his shift, Sen. Donnelly said the Supreme Court arguments heard last week had largely helped change his mind too.

"With the recent Supreme Court arguments and accompanying public discussion of same-sex marriage, I have been thinking about my past positions and votes. In doing so, I have concluded that the right thing to do is to support marriage equality for all," the Senator wrote on his Facebook page this morning.

Today's announcements follow similar ones over the past two weeks.

In two weeks alone a notable eleven Senate Democrats have come out and flipped to now embrace same-sex marriage. Two Republican Senators, Sen. Rob Portman, R-OH., and Sen. Mark Kirk, R-IL., have also embraced marriage equality, splitting with their party.

These numbers contributed to bring a first for the U.S. Senate this week - for the first time a majority of Senators in the U.S. Senate now support marriage equality - 53 Senators, of them two Republican Senators.

With the momentum from these switches the pressure now turns to the dwindling group of whom within the Democratic caucus, has yet to switch positions and come out to endorse same-sex marriage.

The four Democratic senators still opposed are Joe Manchin of West Virginia, Mary Landrieu of Louisiana, Mark Pryor of Arkansas and Tim Johnson of South Dakota.

The pressure from gay rights supporters pressure is now those four Democratic Senators who have not budged from their opposition to gay marriage as they are being singled out more now for their lack of support.