The Democrat's speech in Philadelphia will throw down the gauntlet to Republicans. They insist the priority is cutting the deficit without tax raises, but have yet to say what expenses they'd reduce instead.

That standoff is at the heart of a battle of ideas as the country slides toward both a potential crisis over servicing its national debt and the 2024 presidential campaign.

Biden has still not confirmed his reelection bid but the budget rollout is seen as one more step in the build-up to an announcement.

Because Congress, currently split between Democratic and Republican control, has power over federal taxes and spending, the annual ritual of the White House budget unveiling is more a wish list or policy guide than anything else.

"A budget is a statement of values," Biden said on Twitter.

Main points already teased include a pledge Wednesday from the White House to cut the ballooning federal deficit by $3 trillion over the next decade, in part by raising taxes on the wealthy and corporations. Previously, Biden said he was aiming for a $2 trillion reduction.

At the heart of his proposals will also be a plan to raise taxes on those earning more than $400,000 a year to ensure that Medicare -- the government-funded health care system for people over 65 -- remains solvent.

Hiking the Medicare tax from 3.8 to 5 percent for those wealthy individuals would ensure the program's viability "beyond 2050 without cutting a penny in benefits," Biden said earlier this week.

- Populist pitch -

Republicans have rejected voting for any tax increases, saying Biden is pushing out-of-control spending and anti-business policies.

However, Biden's gambit is that by laying out a deficit cutting plan funded by the very wealthy he will win broad support, while being able to paint his Republican opponents as out of touch.

White House Press Secretary Karine Jean-Pierre said Biden's plan is to make "the wealthy and big corporations pay their fair share, without raising taxes on Americans" earning less than $400,000 a year.

The Republicans, however, will add to the deficit "with handouts to the rich, big corporations and special interest groups," she said.

In Biden's election-ready populist vision, the wealthy are currently getting a free ride, while the struggling middle class just needs a "little bit of breathing room."

But the battle over narratives is far from just academic.

The US Treasury has effectively already run out of money for this year -- and urgently needs Congress to approve taking on extra debt or risk plunging the economy into crisis.

The previously approved $31.4 trillion borrowing ceiling maxed out in January. If the borrowing limit is not increased or suspended before current emergency measures expire, then the US government could default on its obligations for the first time.

That doomsday scenario could kick in as early as July, the Congressional Budget Office said in February.

Republicans say the ever-growing federal debt points to the need for slashing spending, but Democrats say Republicans are using the issue as a way to weaken Medicare and other long-popular programs