Big news in the marriage equality debate: Republican Sen. Mark Kirk endorsed same-sex marriage today, becoming the second Republican senator to do so.

Kirk's announcement follows on the heels of Democratic Sen. Tom Carper's own evolution on the issue. Together, the two senators boost the total number of supporters in the U.S. Senate to 50, giving marriage equality supporters a working majority on the issue (thanks to 51st vote Joe Biden). Rob Portman (R-Ohio) was the first Republican to endorse marriage equality, crediting his son, who is gay, with changing his mind.

The question now becomes whether Kirk and Portman's support will spread to other Republican legislators (both nationally and here in Illinois). The Illinois Senate passed legislation to legalize same-sex marriage in February, but it hasn't yet passed the House, despite Illinoisians' strong support of marriage equality.

It's unclear whether there are enough supporters in the Illinois House to pass marriage equality before the end of the current session. Here's a look at the statewide breakdown by the numbers.