Gov. Mark Sanford’s key legislative priority — a proposed income tax cut — looked all but dead Wednesday night as GOP senators failed to rally enough votes to end a Democratic filibuster of the plan after seven hours of debate.

Democrats locked down the Senate for a second day blocking a vote of the plan, which they say would financially ruin state government. Republicans, who favor the plan and have a majority in the Senate, attempted to up the ante by invoking a rarely used rule requiring all senators remain in the chamber.

But by 7:45 p.m., Republicans had failed in three attempts to get the 28 votes needed to end the Democrats’ stonewalling and decided to adjourn for the night. Republicans needed all 27 GOP members and one Democrat to vote against the Democrats’ block.

Republicans said they didn’t see the need to force senators to stay late when they didn’t have the votes. Some said they might be able to get the needed support overnight.

Others were not as optimistic.

“What it does is, it kills the bill,” said Sen. David Thomas, R-Greenville, a staunch supporter of the tax cut. “I have no expectation we can pick up one vote from the Democrats.”

Sen. John Land, D-Clarendon, who led the opposition to the tax cut, called the day a victory for all South Carolinians. He said Republicans secretly agreed with the Democrats and that was why they gave in early in the evening.

“This was wrong for South Carolina,” Land said. The Republicans “can call us tax-and-spend Democrats all they want, but we have saved them from their own mad device.”

Some Republicans said as they left Wednesday night that if they can’t get the votes, they should move on. There are just four more days until the legislative session ends June 3. In addition to the tax cut, the Senate has yet to deal with most of the major issues in the Legislature this year, including civil court reform, government restructuring and much of Sanford’s agenda.

Sanford spokesman Will Folks said the governor would continue to work overnight to get the support he needs. He blamed arcane Senate rules that allow a minority to block a bill the majority favor.

Sanford’s plan would cut the state’s 7 percent income tax to 4.75 percent in increments over 10 years. Under a version of the plan approved by a Senate committee, the cuts would only come when revenues grew by at least 3 percent.

Opponents say it would benefit only the wealthiest taxpayers — who pay the most tax — and force the state to cut already-lean funding for schools and other services.

But Sanford and other Republicans say it would stimulate the economy and help small businesses grow and hire more employees.

The filibuster and the rule requiring senators to stay in the chamber made for an odd day.

Sergeants at arms were stationed at each entrance, and senators were limited to the floor, side lobbies and the anteroom — with access to restrooms.

Early in the evening, senators used to being able to wander outside to smoke or talk with lobbyists, milled around in the anteroom, chatting with staff. But most were cheerful.

“I don’t feel caged up,” Land said, grinning. “I can stay caged up as long as (the Republicans) can. I probably can stay longer.”

The Senate will have to deal with the vetoes next, and many say they aren’t sure whether they will get to them until the filibuster ends.

Reach Talhelm at (803) 771-8339 or jtalhelm@thestate.com. Staff Writer Valerie Bauerlein and the Associated Press contributed to this report.