With Congress back in session, Senate Democrats are moving forward on legislation codifying marriage equality into law.

Senate Majority Leader Chuck Schumer in Sept. announced that a vote on the issue would happen "in the coming weeks."

Wisconsin Sen. Tammy Baldwin, a leader on the issue in the chamber, told CNN Mon. that debate could begin next week.

What bill is the Senate taking up? The Respect for Marriage Act, which passed the House in July by a 267-157 vote. (CNN)

What does the bill do? The bill requires all states in the U.S. to recognize marriages performed in other states. (CNBC)

The bill explicitly bars states from denying married couples rights and protections on the basis of race or sex. (CNBC)

The bill also repeals the Defense of Marriage Act, a 1996 law that allowed states to not recognize same-sex marriages. (WP)

Democrats in Congress introduced the bill this summer in wake of the Supreme Court's overturning of Roe v. Wade.

In a concurring opinion, Justice Clarence Thomas argued that SCOTUS should "reconsider" its ruling on same-sex marriage.

Thomas: "[Justices] should reconsider all of this Court’s substantive due process precedents, including...Obergefell."

In 2015, the Court ruled 5–4 in Obergefell v. Hodges that same-sex marriages were protected under the 14th Amendment. (CNN)

Sens. Baldwin and Susan Collins are leading an effort to pass the bill in the Senate, where they need 10 GOP votes.

Does the bill have enough support to pass? So far, four Republicans have voiced their support for the bill.

Among them, Ohio GOP Sen. Rob Portman, who reversed his stance on same-sex marriage after his son came out as gay.

Portman is a co-sponsor of the bill, along with Baldwin and Collins. (Congress.gov)

Baldwin's counterpart Wisconsin GOP Sen. Ron Johnson has reversed his position and now opposes the bill.

Johnson told reporters last week that he "never felt this bill [was] necessary." (The Hill)

Negotiations are still underway for the bill: Collins told Politico in Sept., "we’re in pretty good shape."

US support for same-sex marriage is at an all-time high: a May Gallup poll showed 71% supporting same-sex marriage.