A person reads a purchased copy of President Donald Trump's fiscal year 2020 budget request at the U.S. Government Publishing Office (GPO) library in Washington, D.C., on Monday, March 11, 2019.

Critics of President Donald Trump's new budget are accusing him of breaking a key campaign promise ahead of his 2020 re-election bid.

His fiscal 2020 proposal unveiled Monday calls for reductions in funding for Medicare and Medicaid relative to current law. Over a decade, the plan would shave an estimated $800 billion or more off Medicare, which covers older Americans, according to the Kaiser Family Foundation and various reports. It would also cut spending on Medicaid, the federal-state program that insures low-income Americans, by more than $200 billion while setting up block grants to states.

Congress ultimately decides what money to spend, and Trump's proposal is not likely to get through Capitol Hill. Still, a budget represents a president's priorities even if it may not ultimately impact Americans' lives.

For Trump — who during his 2016 presidential bid promised not to cut the popular Medicare, Medicaid and Social Security programs — the proposal opens another vulnerability as he tries to hold on to the White House. In 2015, he declared that he "was the first and only" possible GOP presidential candidate to "state there will be no cuts to Social Security, Medicare & Medicaid."

Trump tweet

Multiple candidates for the Democratic presidential nomination seized on suggested cuts to the social safety net, arguing they would hurt seniors and the most vulnerable Americans. They will likely keep the president's health care policies top of mind through the November 2020 election, after Republican efforts to repeal the Affordable Care Act helped Democrats flip control of the House in last year's midterms.

Democratic presidential hopeful Sen. Kamala Harris of California called the proposed funding reductions "yet another piece of evidence for why we need a new president." Sen. Bernie Sanders, a Vermont independent running for president as a Democrat, framed the floated health-care changes as a "massive transfer of wealth" from the working class to the richest Americans.

Harris tweet

Sanders tweet

Another presidential hopeful, Sen. Amy Klobuchar, D-Minn., pointed to proposed Medicare spending reductions as she contended that "we need a smart budget, not one based on empty campaign promises."

Klobuchar tweet

The proposed Medicare changes aim to address waste and abuse in the system — efforts that both major parties have supported in the past. It is "hard to predict how these proposals would affect patient care if they became law," said Tricia Neuman, director of the Kaiser Family Foundation's Program on Medicare Policy.

However, she expects hospitals and health providers to say the budget will harm seniors. AARP — a special interest group dedicated to older Americans — said it is "concerned about proposed cuts to programs important to seniors" in Trump's budget despite his efforts to address drug prices.

The White House has denied that Trump wants to gut Medicare — a widely popular program.