The Trump administration has submitted to Congress its 2021 budget proposal, a $4.8tn plan which has no chance of passing into law and is instead a purely political exercise, designed to put daylight between the Republican president and whichever Democratic candidate he will face at the polls in November.

To Donald Trump, every event on the presidential stage is now a re-election pitch to voters. Democratic presidential contenders will pick over his budget proposals for lines to attack on the stump.

Trump’s wish list includes a $700bn increase over federal spending in 2018 and represents as clear a statement of Republican priorities as the administration is likely to produce. It includes billions more for defense and a mission to Mars alongside deep proposed cuts to foreign aid and environmental protection and new restrictions on social welfare programs.

On Saturday, Trump tweeted a promise that “we will not be touching your Social Security or Medicare in Fiscal 2021 Budget”.

The proposal released on Monday would nonetheless cut Medicaid spending by about $920bn over 10 years, a reduction in the rate of growth critics warn could effectively reduce funding to dozens of social welfare programs.

Trump would also cut by more than 20% the budget for the Department of Health and Human Services, which includes the agency charged with combating the spread of coronavirus.

Cuts would also include reducing food stamp spending – a key programme for lower-income Americans – by $181bn over a decade. Reforms to medical liability and how hospitals are paid for uninsured care are also proposed though spending on such programs is still projected to rise over a decade.

John Yarmuth, the Democratic chair of the House budget committee, said the budget included “destructive changes … while extending [Trump’s] tax cuts for millionaires and wealthy corporations”.

The House speaker, Nancy Pelosi, called the budget “a statement of values”, adding: “Once again, the Trump budget makes it painfully clear how little the president values the good health, financial security and wellbeing of America’s hardworking families.”

The budget proposes non-defense spending cuts of 5%, to $590bn, and a military spending increase by 0.3%, to $740bn.

It includes a 12% increase to Nasa for proposed travel to Mars and $2bn for Trump’s wall on the US-Mexico border, a reduction on previous requests. Officials have claimed the project is approaching 80% of required budget and said 400 miles of new fence will have been completed by the end of the year.

Within the overall reductions proposed are an 8% cut to education spending, a 13% cut for the interior department, a 15% cut for the Department of Housing and Urban Development and a 26% cut to the budget of the Environmental Protection Agency.

The Environmental Protection Network called the proposed EPA cuts “wholly unacceptable”.

“For the fourth straight year, President Trump has proposed an EPA budget that undermines a half century of public health and environmental gains, and undercuts the agency’s ability to protect people’s health and the natural world that sustains us,” the environmental lobbying body said in a statement.

“undermines a half century of public health and environmental gains, and undercuts the agency’s ability to protect people’s health and the natural world that sustains us.”

If passed, Trump’s budget would have little impact on the federal deficit, which the administration has promised to eliminate by 2028, a goal it has now sidestepped for the third time in as many years.

White House officials claimed their budget proposal would close the deficit by 2035. Even that would be unlikely if the budget ever went into effect, since it would require the US economy to grow at 3% for five years, a rate it has not hit since Trump took office.

Trump has presided over ballooning government debt. In 2017 he said he aimed for a budget deficit of $456bn by 2021. The shortfall is now more than double that figure.

According to the nonpartisan Congressional Budget Office, the deficit is projected to reach $1.02tn this year, as spending of $4.6tn outpaces $3.6tn in tax revenue.

During Barack Obama’s last year in office, the deficit was less than $600bn.