As sixteen states and a host of private parties challenge President Trump’s emergency declaration in court, it seems timely to consider the other avenue for reversing his decision:  congressional override.  Although the odds likely are against such an override, the threat of one could affect how the Administration chooses to implement the President’s declaration.  It also could significantly alter other aspects of the legislative process.
     To appreciate how Congress might intervene, it is important to understand precisely what the President has done.  To obtain funds for a border wall that Congress has refused to fund, the President has directed the Secretary of Defense, in cooperation with other cabinet secretaries, to build the wall by transferring funds from other accounts for which Congress has appropriated funds.  His declaration does not specify how much will be diverted or from which accounts, but the accounts most obviously in jeopardy are those for various military construction projects.  Although the Administration has thrown around various numbers, the declaration itself does not specify a total amount transferred.  
     Two key features of this process bear keeping in mind.  First, only unobligated funds may be transferred.  This sounds straightforward:  he may not pull away funds that the government is already legally obligated to pay contractors.  In practice, determining which funds are and are not obligated can be exceedingly difficult, even for experts.  If the Administration adopts an aggressive definition of what funds are unobligated, it may face a separate round of lawsuits from contractors and others who disagree.
     Second, this process creates losers.  Money diverted to be spent on the wall cannot be spent on the intended projects.  And those projects would not be in appropriations acts if they did not have significant political support, very much including Republican support.  The Administration therefore has a choice:  divert token amounts, allowing the President to claim he defied Congress and started building the wall, or divert more substantial sums and risk alienating the political constituencies for the projects he is defunding.
     Congress has two obvious ways to respond.  The one receiving the most attention involves section 202 of the National Emergencies Act, a trans-substantive procedural statute designed to give Congress a say in the exercise of emergency powers granted to the president under a wide range of statutes.  Originally it allowed a concurrent resolution passed through the two chambers to override an emergency declaration.  After INS v. Chadha invalidated legislative vetoes, Congress rewrote the statute procedures to require enactment of an override as a statute, giving the president the opportunity to veto.  This certainly reduces the chance that a highly politicized emergency declaration will be overridden.  These procedures do, however, have the potential to put significant pressure on the President and his supporters.
     Even though Chadha prevents the Act from bypassing the presidential veto, it does provide critics of an emergency declaration protection against other procedural obstacles, notably the Senate filibuster.  The Act’s mechanics are not quite as automatic as those of some other filibuster-evading procedures – those protecting annual budget resolutions, budget reconciliation acts, military base closure recommendations, and overrides of disfavored regulations – because drafters felt the need to preserve a wider range of choices for Congress.  Most obviously, Members may disagree on when a declared emergency should end.  They also could disagree about whether to terminate all or only some of the emergency powers the president has claimed.
     Nonetheless, the process limits many of the usual opportunities for procedural delay.  When one or more resolutions terminating the declared emergency are introduced in a chamber of Congress, those resolutions are referred to the committee of jurisdiction.  That committee has fifteen calendar days to report out at least one such resolution.  Even if the committee recommends against the resolution, the full chamber must vote on the resolution within three calendar days.  Thus, neither the Rules Committee in the House nor filibusters of the motion to proceed in the Senate may prevent a vote by the full body.  At most, Senator McConnell could ask the relevant committee to report out a very weak resolution (perhaps one terminating the emergency long in the future).  Even then, however, the resolution would not be protected from amendment on the Senate floor. 
     If one chamber passes a resolution to terminate the declared emergency, that resolution must be quickly referred to and reported out of committee in the other chamber and, again, brought to a vote of the full body within three calendar days. 
     If the two chambers’ resolutions disagree, a conference committee is to be convened quickly with a short deadline.  Should the conference committee not reach consensus in time, the resolutions would return to the two chambers “in disagreement.”  This effectively means that each chamber gets back its version of the resolution with the other chamber’s version as a pending amendment.  In theory, the resolution then could “ping-pong” back and forth between the two chambers indefinitely.  But for that to happen the members in each chamber would have to vote repeatedly, making their positions clear.  A large part of how Senator McConnell held Republican senators together during this winter’s shutdown was by shielding them from having to cast difficult votes.  He will lack that ability here. 
     All this should be considered in light of the rest of the on-going legislative agenda, which provides the more promising avenue for reining in or terminating the emergency declaration.  In particular, the President’s emergency declaration is likely to become a central point of controversy in the appropriations process.  This could occur in several ways. 
     Congress could, of course, include in next year’s appropriations legislation a prohibition on transferring or reprogramming funds to build the wall.  So soon after this winter’s disastrous government shutdown – and barely thirteen months from the 2020 election – the President and his allies might be leery of provoking another shutdown over essentially the same issue. 
     Alternatively, if Senator McConnell succeeds in rallying Republicans to block a complete override of the emergency declaration, Congress might a more selective approach.  Members of the Military Construction, Veterans Affairs, and Related Agencies appropriations subcommittees chose those assignments because they are heavily invested in the programs that the President intends to defund.  Democrats on the House floor presumably will strongly oppose appropriating any additional funds for accounts that the President has diverted to fund Wall construction unless such transferring or reprogramming is expressly prohibited.  Lawyers inside and outside of Congress also will work on lists of accounts that the President might seize even if he has yet to do so.  Given this Administration’s fondness for tendentious legal theories, this list is likely to be a long one.  Appropriations for those accounts likely will not be able to pass the House without ironclad language prohibiting transfers or reprogramming. 
     Military construction programs typically spend money quite slowly because of the need to seek bids for contracts and the time required to complete often-complex projects.  This may mean that a fair amount of money is in the pipeline for the President to seize.  On the other hand, it means that if these accounts become seen as backdoor vehicles for funding the wall, a failure to appropriate further funds for them will hobble projects important both to the Pentagon and to many members of Congress for many years to come.  This suggests that, once the accounts being depleted become known, many Republicans may become tempted to support a less-conspicuous override of the President’s action through the appropriations process.  This, probably more than any principled concerns about expanding presidential power, is the greatest threat to Republican solidarity behind the President’s emergency declaration.