House Democrats just wrapped up a 26-hour sit-in, promising to be back at it when Congress reconvenes in July. Technically, this is the second-longest sit-in in modern history — but only because there have been three, and one was a bust.

To learn more about how this compares to other sit-ins, The Fix spoke with Catholic University professor Matthew Green, who is blogging about the sit-in's impacts for The Washington Post's Monkey Cage blog.

Sit-ins require a Goldilocks-like mix of public opinion, media attention and timing to be successful. All three that Green recorded happened in a presidential election year or a few months away from one. All three involved the minority party standing up for something, they argued, the public strongly supported as well. All three came at or close to a planned recess. But not all three had the same sustained media attention. This last one in particular had the advantage of allowing every lawmaker on the floor to broadcast events to the world with his or her cellphone.

Here are the details of the three sit-ins, as relayed to The Fix by Green.

1995: House Democrats demand a budget agreement

How it got started: In the fall of 1995, House Republicans adjourned Congress without an agreement with President Bill Clinton on how to keep the government open. House Democrats were on the floor reprimanding Republicans for not compromising more when, suddenly, Republicans announced that Congress was adjourning. The government was about to shut down, after all. Enraged, Democrats kept talking on the House floor — and a spontaneous sit-in started.

"It just sort of spread by word of mouth: 'Hey, come to the floor,' " Green said.

How it ended: It fizzled after a few hours. Media is like oxygen to sit-ins, and Green said the national press quickly turned its attention to the war of words between Clinton and then-House Speaker Newt Gingrich (R-Ga.). There was so much drama that House Democrats sitting in a shutdown Congress were kind of an afterthought at that point.

2008: House Republicans demand a vote on easing oil prices

How it started: In the summer of 2008, it was House Republicans' turn to seize the floor from Democrats, who were in the majority then. Republicans wanted Democrats to allow a vote to expand oil and gas drilling to help alleviate $4-a-gallon prices.

This sit-in, too, was spontaneous. As Congress was about to break for its monthly August recess, Rep. Tom Price (R-Ga.) essentially said: "Hey, let's not leave. Let's stay," according to Green.

So they did. But it was a different kind of sit-in than the one Democrats held over the past day. Instead of literally sitting on the House floor, House Republicans set up a system where they would conduct a quasi-Congress on their own. Each day during the month-long break, a Republican lawmaker acted as chair, presiding over others who gave speeches — anywhere from five to 20 speeches on a given day. All told, Green calculated, more than 120 House Republicans gave at least one speech during their takeover of the House. Republicans even invited members of the public onto the House floor — which is generally a no-no — to have an audience. (Green was one of them.)

How it ended: House Democrats came back from their month-long break and agreed to hold a vote on oil prices — but it was a symbolic vote that didn't really include any of the policies Republicans had spent the past month advocating for.

2016: House Democrats demand a vote on gun control measures

How it started: This one was much less spontaneous. The Post's Paul Kane reports the idea for a sit-in was borne out of a desire from House Democrats to make a bold play on forcing Republicans' hands to vote on gun control.

They settled on a sit-in and got the backing of Rep. John Lewis (D-Ga.), a civil rights icon who has done a sit-in or two in his life. After the House gaveled in for morning prayers and the Pledge of Allegiance on Wednesday, Lewis and about a dozen other Democrats simply stood up and announced they were taking it over.

They spent the next nearly 26 hours on the floor demanding action on gun control votes. Hundreds of House Democrats and some Senate Democrats joined them. The C-SPAN cameras went off (House rules when Republicans gaveled the chamber out of session in the chaos). But this is 2016, so the world watched the action via live-streaming from lawmakers' phones. The sit-in got wall-to-wall media coverage into the wee hours Thursday.

How it ended: But by Thursday after lunchtime, Lewis announced that it was over — a decision brought about after much negotiating among House Democrats. It probably didn't help that the Supreme Court just handed down two major rulings on affirmative action and President Obama's immigration actions that quickly became the big political story. Also, the House had previously scheduled a week-long recess, and Lewis promised to press the issue during the break back home.

The sit-in was an excellent tactic to rally Democrats' base and get them more excited about pursuing gun control policies. But it's doubtful that it will lead to any changes on actual gun policy.