But from the administration's "skinny budget" released in March, as well as scattered leaks to the press by the administration and Congress, we have a pretty good idea what might be in it:
- An assumption of 3 percent annual economic growth due to tax cuts, which reputable experts say is spectacularly unlikely; 1.8 percent growth is what real forecasters project.
- "Trillions" in cuts to various programs, including, "food stamps, Medicaid and federal employee-benefit programs." The Medicaid cuts are above and beyond the $880 billion in ten-year cuts contained in the Republican health bill.
- Billions in cuts to life-saving biomedical research at the National Institutes of Health
- Big, unnecessary increases to Trump's pet programs, including a nearly 9 percent increase in defense spending, a 7 percent increase in funding for the Department of Homeland Security (including border wall and deportation funding) and a 6 percent increase for the Department of Veterans Affairs.
- Almost comically large cuts to every other federal agency: a 31 percent cut to Environmental Protection Agency budget, 21 percent to Agriculture and Labor, 18 percent to Health and Human Services, 16 percent to Commerce, 13 percent to Housing and Urban Development, 13 percent to Transportation, and 12 percent to Interior.
- A particularly massive 28 percent cut to the State Department, in particular foreign aid funding that even conservative foreign policy types think is essential.
- New funding for voucher programs and private schools alongside a nearly 14 percent cut to the Education Department, including eliminating loan forgiveness for students who go on to do public service.
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This is not a serious plan. It is not something that has much, or any, shot of becoming law. And while that in itself is not too remarkable in a budget document, the fact that an administration is putting out a doomed policy proposal this egregiously unpopular and easy to attack is remarkable.
The budget is a political non-starter
For one thing, most of these changes would require passing appropriations bills, which can, and definitely would, be filibustered by Democrats in the Senate. Slashing the EPA budget or cutting the Department of Agriculture by 21 percent or funding a border wall — that would all have to go through a process that requires 60 Senate votes, and it's simply inconceivable that eight Democrats would defect and support cuts and immigration crackdown funding this draconian.
As the White House learned in the end-of-April government shutdown fight, the filibuster gives Democrats a ton of leverage on run-of-the-mill funding issues. In that dispute, Republicans tried to win a phaseout of Planned Parenthood spending and funds for a border wall, and got neither. The threat of a Democratic filibuster in the Senate was too powerful.
What's more, a lot of this policy agenda is certain to engender vehement opposition from Republicans in the House and Senate. Sen. Lindsey Graham (R-SC) has already declared the cuts to the State Department "dead on arrival." While Republicans on the Hill are generally eager to cut the EPA, some have said they think Trump's desired cuts go too far. Rep. Mike Conaway (R-TX), the chair of the House Agriculture Committee, condemned Trump's proposed cuts to the Agriculture Department. Sen. Rob Portman (R-OH) has recoiled at the Medicaid cuts in the House health care bill, suggesting he'd oppose further cuts in a spending package.
There are ways around the filibuster barrier. The most obvious is budget reconciliation, the special process currently being used to shepherd through the health reform package. That allows policymakers to pass legislation with only 51 votes in the Senate, evading a filibuster. But there are severe restrictions on what the process can be used for. In general, for reasons relating to which committees get "reconciliation instructions," it likely can't be used for regular appropriations, making programmatic cuts like the ones Trump wants for the Agriculture Department or State, or funding boosts like one for a border wall, untenable.
Most importantly, you can only use reconciliation once per fiscal year. The plan had been for the FY2017 reconciliation bill to be health care reform, and then FY2018 bill to be tax reform. Designing a tax reform package is extremely tough, with Republicans disagreeing about whether to adopt "border adjustment," whether to let companies deduct interest payments on debt, whether to include the child care provisions Trump wants, whether to cap itemized deductions, and many, many more.
Adding drastic new budget cuts on top of that carries some advantages with it. The cuts could help pay for a tax reform plan that actually cuts revenue, rather than being revenue-neutral. But putting together a tax plan is a delicate enough endeavor without introducing a lot of contentious issues surrounding how much to cut Medicaid and food stamps and other "mandatory" programs which the reconciliation process can cut. Using the process for cuts as well as taxes could make achieving each vastly harder.
The political logic behind the budget is baffling
All of which raises the question: if these proposals are basically doomed, why is Trump making them? In the case of the Obama administration, this wasn't a hard question to answer. After Republicans retook the House in 2010, most of Obama's legislative agenda was doomed.
But he still put together proposals like the American Jobs Act (a $447 billion plan to cut payroll taxes and fund billions in infrastructure and other stimulus spending), universal pre-K for 4-year-olds paid for by a cigarette tax hike, a "Buffett rule" to increase taxes on the very wealthy, and wage insurance to help unemployed people who take a new job paying less than their old one.
Obama didn't propose these plans because he thought they could pass. He knew very well they couldn't. But he also knew that they were popular, and easy things for him and other Democrats to campaign on. People love to hear that the president wants to spend money to give them jobs in tough economic times, to make the rich pay their fair shares, to help their young kids get to pre-K without paying exorbitant tuition.
That's why Obama made doomed proposals. So why is Trump doing it? These plans are hardly crowd-pleasers. Sure, he ran on the border wall, and defending veterans. But slashing Medicaid? He explicitly promised not to do that. Cutting the Agriculture Department? That's a slap in the face to pro-Trump states like Iowa with large farm industries. Slashing medical research? That's something it's easy for patient groups to mobilize on, with very little to no political upside for Trump.
The best explanation I can see is that Mick Mulvaney, Trump's budget director, is a true believer, a Tea Party type genuinely motivated by an urge to slash federal spending. That's his prerogative, and there's no indication Trump himself is interested enough to force Mulvaney to change course. But if Trump just keeps allowing the conservative hardliners on his team to define his budget policy, he'll be giving his political opponents easy material to campaign on without getting anything in return.
Commentary by Dylan Matthews, senior correspondent at Vox. Follow her on Twitter @dylanmatt.
For more insight from CNBC contributors, follow @CNBCopinion on Twitter.