President Trump’s budget nominee will be on the hot seat on Tuesday.

Liberal senators, most notably Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE (I-Vt.), are expected to grill Rep. Mick Mulvaney (R-S.C.), Trump’s controversial pick to head the White House Office of Management and Budget.

Sanders, the ranking member on the Budget Committee, has kept a relatively low profile since Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE’s defeat in the November presidential election. But the 2016 candidate and outspoken advocate of Medicare and Social Security is gearing up for a battle with Mulvaney.

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During his short career in the House, Mulvaney has led calls to reform Medicare and Social Security. In April 2011, he criticized then-House Budget Committee Chairman Paul Ryan Paul Davis RyanAt indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates Peterson faces fight of his career in deep-red Minnesota district MORE’s (R-Wis.) budget for not going far enough to overhaul Medicare and called for raising the Social Security retirement age from 67 to 70.

Those statements will give Sanders a platform to revive the arguments he made during the Democratic presidential primary and press Mulvaney on whether he will adhere to Trump’s hands-off policy on entitlements. Trump repeatedly ruled out raising the retirement age for Medicare and Social Security during his White House run.

Republicans backing Mulvaney, however, note that several Senate Democrats have voiced support for raising the Social Security retirement age in the past. Sens. Tom Carper Thomas (Tom) Richard CarperDemocrat asks for probe of EPA's use of politically appointed lawyers Overnight Energy: Study links coronavirus mortality to air pollution exposure | Low-income, minority households pay more for utilities: report OVERNIGHT ENERGY: Democrats push resolution to battle climate change, sluggish economy and racial injustice | Senators reach compromise on greenhouse gas amendment stalling energy bill | Trump courts Florida voters with offshore drilling moratorium MORE (D-Del.) and 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 in 2011 they were willing to make adjustments to the program if then-President Obama endorsed them.

One GOP source pointed to a Harris poll from 2012 that showed 83 percent of Americans supported some Medicare reforms to keep the program solvent.

Mulvaney has endorsed hardball tactics to win spending cuts and other conservative policy objectives and criticized GOP leaders in the fall of 2015 for ruling out the possibility of a government shutdown during an impasse with the Obama administration over the federal debt ceiling.

The 49-year-old Mulvaney is a hero among conservative activists for his willingness to cut through fluffy rhetoric about the need to rein in the federal deficit and his willingness to pressure leaders of his own party.

But some Republican lawmakers think he pushes too hard at times, such as in October 2015 when he suggested that Sen. 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 resign as Senate majority leader if he backed a clean debt-ceiling increase.

Democrats have had no success so far in persuading Republicans to turn against Trump’s Cabinet choices, but Mulvaney may offer them their best opportunity.

They will attack him for his conservative positions on federal spending — his support for raising the Medicare and Social Security retirement ages and defunding Planned Parenthood — while also criticizing his failure to pay taxes on a household worker for a period of four years.

Lawmakers will also have a chance to ask Mulvaney about cuts to discretionary spending that Trump transition officials recently discussed within the Office of Management and Budget (OMB), as The Hill exclusively reported last week.

Many of the proposed cuts are based on a budget plan unveiled last year by the Heritage Foundation, which mirrored the budget plan crafted by the Republican Study Committee (RSC), a conservative caucus that includes a majority of House Republicans. Mulvaney in 2015 voted for the RSC budget for fiscal 2016.

Already, Senate Republicans are balking at some spending cuts backed by the RSC, such as eliminating subsidies for rural airports serving sparsely populated communities and the Department of Agriculture’s catfish inspection program.

Senate Democratic 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 (N.Y.) on Sunday highlighted Mulvaney and Rep. Tom Price (R-Ga.), Trump’s pick to head the Department of Health and Human Services (HHS), as two of the most objectionable nominees.

Democrats will attempt to pressure Republicans to vote against Mulvaney by pointing to past opposition from GOP senators to Cabinet picks who failed to pay taxes for hired help.

“Mulvaney, for instance, for four years didn’t pay taxes on a household employee,” Schumer said Sunday on NBC’s “Meet the Press,” comparing it to the tax problems that derailed former Sen. Tom Daschle’s (D-S.D.) bid to become HHS secretary in 2009.

Zoe Baird, President Bill Clinton William (Bill) Jefferson ClintonD-Day for Trump: September 29 Trump job approval locked at 42 percent: Gallup If Trump doesn't know why he should be president again, how can voters? MORE’s nominee for attorney general in 1993, withdrew from consideration in the face of Republican opposition after admitting to not paying Social Security taxes for her family’s chauffeur and nanny.

Democrats are likely to point out that Mulvaney spoke on the House floor in April 2015 in favor of the Federal Employee Tax Accountability Act, which would have barred any individual with “seriously delinquent tax debt” from serving in the federal government.

Democrats argue that Mulvaney would not be eligible to head the OMB had the bill become law.

A Trump transition official said Monday that Mulvaney addressed the tax problem as soon as he learned of what he called “the oversight.”

“Mulvaney paid the payroll taxes as soon as he became aware of the oversight. The language in the Federal Employee Tax Accountability Act of 2015 wouldn’t have applied to Mulvaney because he paid it as soon as he was aware of the issue,” the official said. “There was no lien or court proceeding as stipulated in the bill. The legislation also gave employees 180 days to resolve matters.”

Mulvaney’s Budget panel hearing is scheduled to begin at 10:30 a.m. Tuesday. Five hours later, he will appear before the Senate Homeland Security and Governmental Affairs Committee.

Republican lawmakers are divided over whether to go near Medicare reform in the 115th Congress, remembering the issue has hurt them in past elections, notably the 2012 presidential contest when Democrats ripped Ryan, who was Mitt Romney’s running mate, over his proposed changes to Medicare

Senate Health, Education, Labor and Pensions Committee Chairman Lamar Alexander Andrew (Lamar) Lamar AlexanderTrump health officials grilled over reports of politics in COVID-19 response Now is the time to renew our focus on students and their futures CDC says asymptomatic people don't need testing, draws criticism from experts MORE (R-Tenn.) says Republicans should stay away from Medicare for the time being and focus on putting together legislation to replace ObamaCare.

He noted that Trump promised during the campaign not to cut Social Security or Medicare.

But Senate Republican Conference Chairman John Thune John Randolph ThuneThe Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump contradicts CDC director on vaccine, masks Senate GOP eyes early exit MORE (S.D.) acknowledged that Medicare needs to be addressed in the near future.

“It’s hard to [envision] a scenario where you really do something serious about the deficit without figuring out how we make these programs more sustainable and more cost effective,” he said. “The big money in the budget is entitlement spending and mandatory programs, and at some point we have to tackle that.”

A few months after Mulvaney won election to the House in the Tea Party wave of 2010, he declared: “We have to end Medicare as we know it. We have to fix it.”

He said not raising the Medicare retirement age in light of increasingly longer life expectancy was “missing the 800-pound gorilla in the room.”