There was no pressure... Democrats are allowed to "evolve" as they wish on any issue.
“If there’s tension between Johnson’s public position and his private opinion, he’s not alone. Landrieu has straddled that line, telling BuzzFeed Saturday, “I feel very strongly that people should be allowed to love who they love, but unfortunately my state has a very strong ban against gay marriage constitutionally.” Not only that, but last month a Public Policy Polling survey found that just 29 percent of Louisianans back gay marriage.”
I doubt Mary Landrieu is going anywhere near the Gay Marriage issue and will Tip-Toe around any form of Gun Bans (including high capacity magazines). She's enjoyed a long Political Career, at one time she was even considered for Kerry’s Running Mate. She is up for Re-election and knows this could possibly be Political Suicide for her.
Yes I will be following this as well. The complex issue would be what the status would be as regards legal rights and other concerns if a marriage was recognized in one state but not in another. There would need to be specific legislation to address this.