As appropriators try to build on the accord they reached in the $1.1 trillion omnibus while working on fiscal 2015 spending plans, some observers already are questioning whether the largest nondefense spending bill, Labor-HHS-Education, can be completed as a stand-alone measure in a steeply divided Congress.

“That’s the tripwire,” said South Carolina Republican Lindsey Graham, a member of the Senate Labor-HHS-Education Appropriations Subcommittee. “I think you can get almost every other bill passed except that one.”

The measure, set at $158 billion in the current fiscal year, is a stark example of the chasm between the parties on social issues. It funds the programs that are anathema for Republicans but bread-and-butter for Democrats, including public broadcasting, labor initiatives and, most prominently, portions of the 2010 health care law (PL 111-148, PL 111-152).

The divide between the parties has made the bill more of a blueprint for lawmakers’ strict policy priorities than a vehicle to enact funding; during the fiscal 2014 appropriations cycle, House and Senate appropriators worked using top lines for the measure that were more than $40 billion apart.

That divisive history is what made the inclusion of a fully formed Labor-HHS-Education measure in the omnibus (PL 113-76) all the more surprising.

Top appropriators, including Senate panel Chairwoman Barbara A. Mikulski, D-Md., say they want to get the measure enacted this year — for just the third time since 2002 — under a more normalized process.

But that will be a “tough slog,” said Jim Dyer, a former GOP staff director for the House Appropriations Committee who is now at the Podesta Group. “There’s enough stuff in there to discourage anybody,” he said.

The challenges facing the bill start with funding levels. The December budget agreement (PL 113-67) set aside $492.5 billion for domestic programs, but the Labor-HHS-Education title must compete with other domestic priorities.

Republicans will try to funnel money to items such as homeland security and weapons programs at the Department of Energy, while Democrats will move to protect President Barack Obama’s domestic priorities such as early childhood education and the Dodd-Frank financial regulatory overhaul (PL 111-203).

Labor-HHS-Education programs have lost the funding battle in recent years and the bill’s many social programs may fall behind again in fiscal 2015, according to Rosa DeLauro of Connecticut, ranking Democrat on the House Labor-HHS-Education Appropriations Subcommittee. “We just keep lowering the standards,” she said, pointing to numbers going back to 2010.

But the funding levels aren’t really the major problem with what lawmakers call “Labor-H.”

Because it houses so many social programs, the bill is a lightning rod for battles over social issues. And the lure of election-year messaging may make spending bills like Labor-HHS-Education a magnet for the sort of steeply divisive policy riders that have doomed such measures in the past — particularly after the rush to complete the omnibus in January locked out policy amendments, leaving many members angry. “There’s probably some pent-up frustration on the side of the Republicans because the omnibus was done behind the scenes with no amendments,” said Joel Packer, co-chairman of NDD United, a coalition group that pushes for more domestic discretionary spending.

If appropriators are serious about bringing Labor-HHS-Education to the floor this year, they may have to forge another agreement to limit policy riders, much as Mikulski and her House counterpart, Harold Rogers, R-Ky., did during the omnibus negotiations, budget watchers said.

“I think it’s the only way to get a bill like this done in an election year,” Dyer said. “The tendency in this institution is to try to force these so-called political votes.”

The broader fights over spending levels could be diffused if Rogers and Mikulski break with custom and pre-conference their top-line allocations for the 12 spending bills, known as 302(b) levels, said House appropriator Tom Cole, R-Okla.

“If we’re working off a common number, and people know that if we could just get it to conference, these conferees can really work these things out and our chances of actually moving a Labor-HHS-Education bill go way up,” Cole said.

Even if House and Senate appropriators can move the bills through their respective committees, leadership priorities will decide their fate after that. That’s particularly true in the Senate, where Democrats’ control of the chamber is at risk in the November elections.

“The question is whether the Senate majority leader wants to bring this bill to the floor and to push it through the system in an election year where his priority is probably retaining the Senate,” Dyer said of Nevada Democrat Harry Reid. “We don’t have the answer to that yet, but at the end of the day, that’ll be the core question.”

Sen. Tom Harkin, D-Iowa, chairman of the Labor-HHS-Education Appropriations Subcommittee, said his bill could pass if leaders allow it to reach the floor.

“The Defense appropriations bill is the bill that defends America, but the Labor-HHS bill is the bill that defines America,” said Harkin, paraphrasing Daniel K. Inouye, the late Senate Appropriations chairman. “I want to define. I want to bring it out as a definition of who we are and what kind of society we are. Let’s see how much they really want to go after all these programs. I think we’ll be fine if we bring it up to the floor. We shouldn’t be afraid.”

Top appropriators are keeping their plans for the bill close to the vest. Rogers said completing a Labor-HHS-Education bill is possible but would “take a lot of work.”

“With it being an election year, it makes it more difficult,” he said.

Georgia Republican Jack Kingston, chairman of the House Labor-HHS-Education Appropriations Subcommittee, put the chances of the bill’s enactment at “50-50.”

“It’s not going to be easy, but you try to do what you think is best,” said Kingston, who indicated the measure would likely be one of the last to be considered.

Some advocates of domestic programs said their expectations are not very high for the bill. Packer said he expects a continuing resolution, at least until after the election, and the fate of the underlying programs for the rest of fiscal 2015 will likely be determined by the November elections.

“Because the top-line number for nondefense discretionary is virtually the same for fiscal 2015 that it was for 2014, if you have a CR the numbers wouldn’t be that different than if you had a regular appropriations bill, to be honest,” Packer said. “It’s not like there’s a big pot of extra money lying around.”

But Cole said clearing the bill would send a strong message to constituents who have tired of congressional gridlock. “It would be a gesture of goodwill and a huge sign that we’re returning, step by step, to regular order and that we’re actually doing what the American people expect us to do, which is to compromise,” he said.