Virginia’s General Assembly will begin a special session Wednesday to hammer out a deal for a two-year, $85 billion state budget.

Most of the commonwealth’s 140 legislators will stay home. But 12 negotiators — Republicans and Democrats, delegates and senators — will return to Richmond to try to draft a spending plan that can pass both chambers. The General Assembly has busted budget deadlines before. But in those instances, the House and Senate had each passed a budget and only had to work out the differences. This time, only the House has a plan in play. Here’s a primer on the coming negotiations.

THE IMPASSE: Republicans have a 2-to-1 House majority and control the evenly divided Senate by virtue of Lt. Gov. Bill Bolling’s power to break ties. But Bolling lacks the authority to vote on the budget, so Republicans need at least one Senate Democrat to vote with them. Although a couple of conservative Democrats sided with Republicans on bills to restrict abortion rights and expand gun rights, the party’s senators stuck together on the budget and refused to support one during the regular session, which ended March 10. Democrats have said they will not vote for a budget until their party is given more power on certain Senate committees, which the GOP stacked in its favor with Bolling’s help. Democrats also have demanded more spending on schools and transportation.

AT STAKE: If the state does not have a budget before the new fiscal year starts July 1, a partial government shutdown could take place. That would be a first for Virginia, whose constitution says that only the General Assembly can appropriate state money. State officials say it is not clear how funding for even essential services, such as police and prisons, could legally continue, although they also say they would have to find a way. But transportation projects could be shut down, state employees furloughed and tax refunds delayed, among other things. The state’s top-notch credit rating could take a hit, too.

THE OPTICS: Republicans have painted Democrats as power-hungry obstructionists for refusing to help pass a budget, arguably the most important business before the General Assembly. Those charges could stick if the stalemate drags on and Virginians are affected by budget uncertainty or a shutdown, political observers say. Republicans, at the same time, risk Virginia’s reputation as a well-run state as Gov. Robert F. McDonnell seems to angle for a vice presidential berth and tries to deliver the state for the GOP in presidential and U.S. Senate races.