Because, this means the Dems can lard (as in sew pieces of fat into a bony piece of meat to make it edible) them
not with pork, but with:
(a) rollbacks of Repug changes to all those health, welfare and environment programs and
(b) explicit removals of presidential power to change or modify them, a la Youngstown Sheet and Tube v. Sawyer category 3 (i.e., where Congress has explicitly spoken, the President's independent power is at its nadir and his ability to act independently is quite limited.).
Under category (a) - you name the environmental, health, educational or public welfare (general "public good" - not "monthly checks") program Bushie and his henchmen haven't gone after to destroy or pervert. The latest - today - is EPA trying to eliminate all national standards for lead emissions. In the dark of night, in a cloud of bluff and bullsh*t.
Roll back the changes, enact the new ones furthering Dem principles, and withdraw the power of the bureaucracy to make new ones against Dem principles.
In category (b), we can start with stuff like forbidding him from conducting any show trials at Gitmo or spending any money on the "court complex" contract, for starters. Then we can move on to things like barring the government from spending any money arguing in Court that, say, state secrets preclude the Courts from addressing the claims of torture by detainees or, say, that the Courts have no jurisdiction over habeas claims by prisoners. (I think the DoJ budget is one of those not yet done....)
They can even include a provision that says "Presidential signing statements are a nullity".
And, if the Dems have the chestnuts to use the conference committees in a manner even remotely close to the way the Repugs did, but more politely, there's no way even Holier-than-thou Sen. Tortureman (CFL-CT) can hold up the budgets.
Here's the syllogism:
Congress re-works the budgets the Repugs punted to enact the Dem policy preferences.
Congress presents Preznit with budget, makes clear "this is the budget you will get".
Preznit refuses to sign budget - it's his fault the government will shut down.
Dems can say: "public - when the parks start closing, call the White House"
Preznit vetoes budget - it's his fault the government will shut down
Dems can say: "public - when the parks start closing, call the White House"
Preznit signs budget and appends signing statements (oops! they're nullities!) and disobeys the budget - well, spending government funds contrary to appropriations is commonly considered, uh, a crime.
Preznit obeys budget - he's neutered.
The Repugs did a great disservice to their Commander-in-Chief. The Dems ought to thank them, as they take advantage of it.