Senators are firing the opening salvos in a new fight over funding the government.

With President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE releasing his first budget request Thursday, both parties are preemptively pointing fingers over who would be responsible if Congress misses a deadline in April to avoid a government shutdown.

Republicans say it’s up to Democrats to play ball, while Democrats counter that Republicans have to be willing to reject some of Trump's proposals.

“If they put those poison pill amendments in and try to shove them down the American people's throats, of course they might be responsible for shutting the government down,” Senate Minority Leader Charles Schumer Chuck SchumerMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security Warren, Schumer introduce plan for next president to cancel ,000 in student debt Schumer lashes out at Trump over 'blue states' remark: 'What a disgrace' MORE (D-N.Y.) told reporters during a leadership press conference.

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Schumer said a letter he and other top Democrats sent to Senate 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.) should serve as a “guidepost” for how Republicans can work with them to avoid a shutdown.

Democrats outlined in the letter, which was also sent to Senate Appropriations Committee Chairman Thad Cochran William (Thad) Thad CochranEspy wins Mississippi Senate Democratic primary Bottom Line Mike Espy announces Mississippi Senate bid MORE (R-Miss.), their demands for any spending bill: that Republicans avoid “poison pills” that would stir ire from Democrats and that any increases in defense spending be matched with a boost in nondefense spending.

“If Republicans insist on inserting poison pill riders such as defunding Planned Parenthood, building a border wall, or starting a deportation force, they will be shutting down the government and delivering a severe blow to our economy,” they wrote in the letter.

Trump’s budget outline — which marks the formal start of budget negotiations between the two ends of Pennsylvania Avenue — drew swift opposition from Democrats, who warned Republicans against funding the president’s border wall or cutting off federal dollars for Planned Parenthood.

“I will oppose efforts to fulfill empty campaign promises at the expense of proven programs that are vital to local law enforcement and national security,” Sen. Dianne Feinstein Dianne Emiel FeinsteinSenators offer disaster tax relief bill Democrats back away from quick reversal of Trump tax cuts Congress must save the Postal Service from collapse — our economy depends on it MORE (D-Calif.) said of Trump’s push to fund the border wall.

Sen. Dick Durbin Richard (Dick) Joseph DurbinMcConnell focuses on confirming judicial nominees with COVID-19 talks stalled Senate Republicans signal openness to working with Biden Top GOP senator calls for Biden to release list of possible Supreme Court picks MORE (Ill.) — the No. 2 Senate Democrat — added separately that “it’s time for Republicans to remember that Congress is an independent branch of the federal government that won’t be bullied into these billion dollar boondoggles.”

Trump’s budget outline calls for deep cuts at department and agencies that would eliminate entire programs and slash the size of the federal workforce, while boosting defense spending.

He also sent a supplemental request for the rest of the 2017 fiscal year, which runs through the end of September. That proposal includes an extra $33 billion for the Pentagon, building a border wall and the detention facility at Guantanamo Bay.

Though Democrats are in the Senate minority, they can block any spending bill they object to by keeping it from getting 60 votes.

In 2015 and 2016 — the first two years that Republicans had controlled the Senate in nearly a decade — Democrats halted progress on spending bills more than a dozen times.

The partisan posturing comes as senators are under a time crunch to fund the government.

Debates over repealing and replacing ObamaCare and Judge Neil Gorsuch’s Supreme Court nomination are expected to dominate much of the Senate’s work heading into early April. Then, senators are expected to be out of town for two weeks and return to Washington five days before the funding deadline.

Republicans are tamping down speculation of a potential government shutdown next month, noting Democrats howled for years after the 2013 shutdown.

“I'm amused by the Democrats apparently warming up to the idea that threatening to shut down the government is a good idea. It seems to me everybody's got kind of memory loss on the other side,” McConnell told reporters.

The government shut down for 16 days in 2013 after conservatives demanded that the spending bill cut off federal funding for Planned Parenthood and stop the implementation of ObamaCare.

McConnell stressed that Democrats would be part of the negotiations over the funding bill.

“They will have an opportunity to ball it up, once again,” he said. “I've been hoping the fever's going to break here at some point and we'll get into an operational mode. ... We haven't seen much of that so far.”

McConnell has repeatedly accused Democrats of suffering from a "fever" since the 2016 elections, which he argues is leading them to oppose almost anything partly in an attempt to satisfy their liberal base.

Republicans will likely get help pressuring Democrats to come to the negotiating table. After top Democrats sent their letter to McConnell, The Washington Examiner floated nicknaming the Senate’s top Democrat “Shutdown Schumer.”

But McConnell will also have to be on guard against any rebellion within his own caucus.

GOP Sens. Lindsey Graham Lindsey Olin GrahamThe Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Senate Democrats' campaign arm announces seven-figure investment to boost Graham challenger Graham: Comey to testify about FBI's Russia probe, Mueller declined invitation MORE (S.C.) and John McCain John Sidney McCainThe electoral reality that the media ignores Kelly's lead widens to 10 points in Arizona Senate race: poll COVID response shows a way forward on private gun sale checks MORE (Ariz.) are expected to push for more defense spending in the funding bill, which would likely face opposition from Democrats.

The Senate will also likely reject at least part of Trump's proposed 28 percent cut to the State Department budget.

McConnell previously said a deep cut to State Department funding likely wouldn’t pass the chamber. Sen. Marco Rubio Marco Antonio RubioFlorida senators pushing to keep Daylight Savings Time during pandemic 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 Intelligence chief says Congress will get some in-person election security briefings MORE (R-Fla.) on Thursday said he opposes the cuts.

Meanwhile, Sen. Dean Heller Dean Arthur HellerOn The Trail: Democrats plan to hammer Trump on Social Security, Medicare Lobbying World Democrats spend big to put Senate in play MORE (R-Nev.) partnered with freshman Democratic Sen. Catherine Cortez Masto (Nev.) to send a letter to Energy Secretary Rick Perry and Mick Mulvaney, the director of the Office of Management and Budget, opposing a provision in Trump’s budget that would restart licensing to store nuclear waste in Yucca Mountain.

Heller is considered one of the most vulnerable senators up for reelection in 2018, with Republicans facing an otherwise favorable Senate map.

Democrats who are up for reelection in 2018 will likely face a mountain of pressure to buck their party and support legislation to avert a shutdown, even if it includes provisions opposed by leadership.

Yet Sen. Chris Van Hollen (D-Md.) predicted that some GOP senators could ultimately become "allies" in the fight because the budget will generate a backlash in states that Trump won in the election.

"If you look at the areas where Donald Trump did especially well, they get especially hard hit by this budget. Rural areas get badly hurt in this budget,” said Van Hollen, who is also the chairman of the Democratic Senatorial Campaign Committee.

Democrats are defending 25 seats in 2018, with both parties keeping a close watch on the 10 states won by Trump that have a Democratic senator up for reelection.

Van Hollen specifically pointed to West Virginia, where Democratic Sen. Joe Manchin Joseph (Joe) ManchinBiden promises Democratic senators help in battleground states Senate leaders quash talk of rank-and-file COVID-19 deal OVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' MORE is considered a vulnerable incumbent next year.

"I think this is going to be a wake up call to a lot of people who supported Donald Trump,” he said. “That his budget is betraying them and the commitments he made."