Democratic demands for $600 million in emergency funding is threatening to take down a bipartisan bill tackling the nation’s growing opioid addition.

Legislation backed by Sens. Sheldon Whitehouse Sheldon WhitehouseLWCF modernization: Restoring the promise Restaurant owner defends calamari as 'bipartisan' after Democratic convention appearance Warren calls on McConnell to bring Senate back to address Postal Service MORE (D-R.I.) and Rob Portman Robert (Rob) Jones PortmanRomney undecided on authorizing subpoenas for GOP Obama-era probes Congress needs to prioritize government digital service delivery House passes B bill to boost Postal Service MORE (R-Ohio) is coming to the Senate floor this week.

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Its passage would be a significant victory for Portman, who is in a tough reelection race this year. It would also be an election-year achievement for the Senate, allowing Majority leader Mitch McConnell Addison (Mitch) Mitchell McConnellMcConnell focuses on confirming judicial nominees with COVID-19 talks stalled McConnell accuses Democrats of sowing division by 'downplaying progress' on election security Warren, Schumer introduce plan for next president to cancel ,000 in student debt MORE (R-Ky.) to argue the chamber is functioning despite the battle over a possible nomination to the Supreme Court by President Obama.

But Democrats are signaling that they’re preparing to fight to include the emergency funding, which is backed by Sen. Jeanne Shaheen Cynthia (Jeanne) Jeanne ShaheenSenate Democrats introduce bill to sanction Russians over Taliban bounties Trump-backed candidate wins NH GOP Senate primary to take on Shaheen Democratic senator urges Trump to respond to Russian aggression MORE (D-N.H.). She represents a state with a serious heroin and opioid problem, something that came to national attention during the state’s presidential primaries.

While acknowledging that his caucus wants to tackle the epidemic, Minority Leader Harry Reid Harry Mason ReidSenate Republicans signal openness to working with Biden Mellman: The likely voter sham Bottom line MORE (D-Nev.) warns that that Shaheen’s amendment should get “every consideration.”

He said this week it is important that words are backed up with “real solutions.”

Shaheen, separately, urged her colleagues to help her get the funding included as part of the Comprehensive Addiction and Recovery Act, or CARA.

A test vote comes on Monday when the Senate votes to end debate on taking up the legislation.

The broader legislation from Portman and Whitehouse would authorize—but not appropriate—funding for programs to combat prescription drug and heroin abuse, in addition to increasing the availability of naloxone, a drug to treat overdose.

Kevin Smith, a spokesman for Portman, noted that millions included in last year’s omnibus bill could be directed to CARA.

Democrats have specifically sidestepped questions on if they’re willing to sink the drug addiction bill, but senators are preemptively trying to shut down a contentious floor fight before it starts and avoid “poison pill” amendments.

McConnell said he’s “hopeful we can reach an agreement to finish this bill with just a handful of amendments.”

Senate aides, separately, suggested that negotiations over a path forward were playing out at the leadership level.

The push to find a deal comes as senators have repeatedly watched similarly bipartisan bills get stalled over unexpected drama on the Senate floor. An otherwise uncontroversial energy bill has been waiting in limbo for nearly a month after a surprise battle broke out on aid for the Flint, Mich., drinking water crisis.

Asked earlier this month if he was worried the opioid bill could face a similar fate, Sen. John Cornyn John CornynAirline job cuts loom in battleground states Senate Republicans signal openness to working with Biden Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll MORE (R-Texas) told reporters “I hope not, we had a pretty good run of productivity on a bipartisan basis last year and I hope we’ll continue that this year.”

But the battle over the opioid bill is playing out amid election-year politics and bleeding into the Republican fight to keep control of the Senate as they defend 24 seats in November.

Portman has touted his support for the legislation as he tries to localize his campaign.

But he’s coming under fire from Democrats both in Ohio and Washington, D.C., who suggest that he’s flip-flopped on the issue.

Greg Beswick, the executive director for the Ohio Democratic Party, suggested that Portman is playing “political games” and using “D.C. double talk.”

“We know that Rob Portman likes to talk about what he’s doing with the crisis but actually refuses to take a stand and provide funding,” he told reporters during a conference call Friday.

Democrats also point to the Republican senator’s stint as the director of the Office of Management and Budget under President George W. Bush, where he helped work on a budget that included cuts to funds for substance abuse programs.

Portman, however, fired back at those charges, suggesting that he has been working to combat drug abuse for decades.

“I suppose they want to play politics with everything these days, but I’m proud of the leadership I’ve shown,” he told The Hill.

Democrats suggest vulnerable Republicans are trying to take credit for helping battle drug addiction while brushing over mixed voting records.

Democrats are also targeting Sens. Pat Toomey (R-Pa.) and Kelly Ayotte Kelly Ann AyotteBottom line Bottom line Bottom Line MORE (R-N.H.), whose races will help decide who controls the Senate next year.

Democrats point to a string of votes in favor of budgets and spending bills going to back to 2011 that included cuts to substance abuse funding. They also point to Ayotte missing a committee hearing on the growing prescription drug abuse problem in mid-2013, but holding a campaign fundraiser with the telecom industry on the same day.

Gov. Maggie Hassan, Ayotte’s likely Democratic opponent, has put countering the epidemic at the center of her race. Her campaign touted articles this week highlighting her efforts to make progress on the issue during the National Governor’s Association annual winter meeting.

Toomey, most recently, voted against the omnibus bill that included extra money for prescription drug and heroin abuse. The Pennsylvania Republican said at the time that he opposed the spending bill because “it does not address our core spending problem.”

Toomey is expected to offer an amendment aimed at making it easier for those who are addicted to get treatment and cracking down on the over prescription of painkillers as an amendment to Portman’s legislation.

Senators are also facing pressure from outside groups to put the politics aside.

Dozens of organizations sent a letter to McConnell and Reid this week urging them to make sure CARA passes, saying it will “make important advancements to effectively address the growing epidemic of drug abuse.”

The Harm Reduction Coalition, separately, sent a letter to Senate leadership urging them to move the legislation in a “bipartisan fashion” and suggesting that some of the programs pushed by Democrats do not “achieve sufficient and timely impact to warrant emergency supplemental appropriations outside of regular order.”

The Centers for Disease Control and Prevention reported last month that drug overdose deaths reached historic levels in 2014, with an individual more likely to die by overdose than in a car crash.

Portman, for his part, stressed that he wants to keep his legislation non-partisan as he tries to get it through the upper chamber, after it passed out of the Judiciary Committee by a voice vote.

“To me it’s never been a political issue,” he said. “I hope they don’t make it one now.”