TALLAHASSEE — It's no longer a debatable claim to say that the 2015 legislative session has ventured into uncharted territory.The session jumped off the rails at 1:15 p.m. Tuesday when Florida House Speaker Steve Crisafulli, R-Merritt Island, told his 119 colleagues in the lower chamber that they were done and could go back home three days before Friday's scheduled end date. The Senate, caught off guard, now plans to finish up Wednesday.It's the first time since the Legislature started keeping records that the chambers will end regular session on different days.So how did we get here? Where are we going? We may not know for some time, but here is a guide.What happened?The Florida House and Senate couldn't negotiate the one piece of legislation they are required to pass: a state budget. The House passed its $76.2 billion budget plan April 2, but it didn't include $4 billion that was included in the Senate's budget, which had passed hours earlier. For a month, the two chambers have not been able to agree on how to bridge that $4 billion gap.Why?There are two main reasons the House and Senate budget proposals were so different: a $2.2 billion federal-state hospital funding program known as the Low Income Pool, and Medicaid expansion. The LIP program provides funding to hospitals that treat large numbers of uninsured and Medicaid patients. It is scheduled to end June 30 under an existing agreement with the federal government. The Senate proposed a successor program and assumed the money would come through. The House did not include any LIP money in its budget. What's more, the Senate's proposed budget included $2.8 billion in federal Medicaid expansion money to provide health care coverage to more than 800,000 low-income Floridians. The House has long opposed that idea, likening it to an endorsement of Obamacare. Over the course of the session, the two sides refused to back off of their positions. They dug in even deeper this month when the federal government said it was more likely to approve a LIP successor if Florida expanded Medicaid.This is all about Obamacare, isn't it?Yes. For the past three years, Florida has refused $51 billion in federal money earmarked for expanding subsidized health care coverage under the Affordable Care Act, making it one of 22 states to do so.Has session ever ended this way before?Records on adjournment dates only go back to 1971, and they don't show this ever happening. The State Library and Archives of Florida don't track records before then. The House did end its regular session 90 minutes earlier than the Senate in 2011, but that was on the same day. The House ended a special session in October 2001 a couple of days before the Senate, but again, that was a special session that didn't have the entire state budget riding on it.How long do they have to agree on a budget?The fiscal year ends June 30.How many bills did they send to the governor before leaving?182 bills passed both chambers.What does Sine Die mean?It's Latin for "without day." It means there's no more time left in the session. The Constitution allows the Legislature to meet for 60 days but doesn't prohibit lawmakers from ending early, before midnight on the last day, which is Friday.Can any more bills be passed?Not in the House, which left with 32 Senate bills still up for a vote, killing them. On Wednesday, the Senate takes up 50 bills already passed in the House. If senators approve the House legislation, the bills go to the governor.What happens next?Even Crisafulli, in a message to his members, said he didn't know when they would return for a special session. Special session can happen three different ways. Gov. Rick Scott can call a special session by proclaiming a stated purpose. The last time that was done was in 2010 when Gov. Charlie Crist called a July 20-23 session on prohibiting offshore oil drilling. It didn't pass. Or Speaker Crisafulli and Senate President Andy Gardiner can call a special session by filing a proclamation with Secretary of State Ken Detzner about its purpose. Or the Legislature can convene when 20 percent of its members file a petition with Detzner stating the purpose of the proposed session. After receiving the requisite number of petitions, Detzner would have seven days to poll the Legislature. If three-fifths of lawmakers agree to the session, then it would take place between 14 and 21 days from the date of the poll.What happens in a special session?During a special session, the only legislative business allowed must be restricted to what was stated in the proclamation filed with the Secretary of State, in a communication from the governor, or in the consent approved by three-fifths of both chambers. Because this upcoming special session must address the budget, it will touch on many issues that are tied to state funding. That should make it more of a mini-regular session than a special session. Unrelated topics — such as how much will lawmakers steer into land acquisition from the use of Amendment 1 dollars — won't get resolved now until special session. It also means lawmakers can negotiate anything into the session using the umbrella of the budget.What happens if they don't pass a budget by June 30?Senate Appropriations Chair Tom Lee, R-Brandon, said that won't happen.Contact Michael Van Sickler at [email protected] Follow @mikevansickler.