In my January 7 post on Trump's potential use of "emergency" powers to build a wall on the Mexican border, I warned that, if he succeeds in this plan, it would set a dangerous precedent that conservatives would have reason to regret the next time a liberal Democrat occupies the White House:

If Trump is able to overcome legal obstacles and use an emergency declaration to secure funds for the wall without congressional authorization and use eminent domain to seize the land he needs, conservatives are likely to have good reason to regret the precedent it would set. The same powers could easily be used by the next Democratic president for purposes that the right would hate.

Consider a scenario where Elizabeth Warren wins the presidency in 2020, but Republicans in Congress refuse to allocate funds she claims are necessary to combat climate change and institute the gigantic "Green New Deal" program many progressives advocate. President Warren could then declare climate change to be a "national emergency" and start reallocating various military and civilian funds to build all kinds of "green" construction projects. She could declare that climate change is a threat to national security, and use the Army Corps of Engineers and other military agencies to participate in the project.

Indeed, the claim that climate change is a menace to national security is at least as plausible as the claim that undocumented immigrants on the Mexican border are. The Obama Administration Department of Defense even published a report on the subject in 2014. And, of course, if President Warren decides she needs to seize some private property to carry out her plans, she could cite the Trump precedent to use eminent domain for that purpose. This is just one of many ways in which liberal Democrats could exploit the sorts of powers Trump claims here. It would not be difficult to imagine others.

Since then, a number of conservative commentators who (unlike me) support the basic idea of building a wall, have also warned against the dangers of setting this kind of precedent for sweeping presidential power. They include David French, Philip Klein of the Washington Examiner, and the editors of the National Review. French correctly cautions that "[e]ach [such] abuse builds on the next; hypocrisy builds on hypocrisy. The only clear winner is the imperial presidency." Klein points out that conservatives could easily end up as long-term losers, even (perhaps, especially) if Trump's emergency ploy stands up in court:

If President Trump tries to invoke emergency powers to build a border wall and fails in courts, it would be bad for conservatives. But if he succeeds in court, it would be even worse....

All cases carry risks for conservatives, as in all cases a substantial number of Republicans and prominent conservatives will inevitably endorse the move, thus weakening their ability to resist the next Democratic president who tries to stretch the boundaries of executive power. However, some outcomes are worse than others.

If the Trump loses in court, the wall most likely will not get built; however, it will have a silver lining of having established a court precedent limiting the use of emergency powers, thus hindering the ability of the next Democratic president to invoke them to advance liberal policy goals....

If the Trump wins in court and the wall gets built, at first blush, that would seem like a home run for conservatives. And it's true that they'd get something they want: a wall. However, in the long run, it also means that it will have established a precedent that will allow the next Democratic president to declare national emergencies to advance liberal policy goals.

That brings us to the final scenario, which would undoubtedly be the worst case scenario for conservatives. In that case, Trump wins the case in court, but the decision comes too late for him to get much construction done by the end of his first term. Then, he loses re-election. The next Democratic president could then stop construction on the border wall but still turn around and use the precedent set by court decision as a means of advancing any big-ticket liberal items that can't get through Congress. In this case, conservatives give the next Democratic president a blank check and don't even have a wall to show for it. Nightmare.

Perhaps most interestingly, GOP Senator Marco Rubio recently warned that the use of emergency powers to build the wall could set a precedent for a Democratic president to use it to deal with climate change:

A national emergency declaration by President Donald Trump over border security could wind up hurting Republicans, GOP Sen. Marco Rubio told CNBC on Wednesday.

The Florida Republican contended that Trump was elected on the promise of building a wall along the U.S.-Mexico border and the president has to "keep that promise." But "we have to be careful about endorsing broad uses of executive power," he added. "I'm not prepared to endorse that right now."

Such a declaration would set a precedent, Rubio said. "If today, the national emergency is border security ... tomorrow the national emergency might be climate change."

Unlike French, Klein, and the National Review, Rubio has not actually definitively come out against using emergency powers to try to build the wall. He only said he's "not prepared to endorse that right now" (emphasis added). But if he and other congressional Republicans are genuinely worried about setting a dangerous precedent, they could (along with Democrats) pass legislation forbidding such shenanigans, and place tight restrictions on the president's power to reallocate funds and condemn property without specific congressional authorization. In my view, using emergency powers to build the wall is barred even under current law. But the relevant statutes are murky enough that misguided judicial deference to executive power might allow Trump to prevail - and thereby set a dangerous precedent for the future.

The flip side of this is that some liberals might actually like the prospect of using emergency powers to circumvent Congress and seize property for the purpose of combating climate change, or other liberal goals. They might even conclude that letting Trump have his "emergency" wall is a worthwhile tradeoff, if a future liberal president can use the same authority to combat global warming.

Unlike the largely bogus "crisis" on the Mexican border, I believe that climate change is a genuine problem (though there is surely room for disagreement about the extent of the risk, and strategies to reduce it). But that doesn't mean that rule by presidential decree is the right way to address it. And given that we still have many years to address the danger, it would be especially wrong to deal with it by means of emergency powers intended to address fast-moving crises that develop too quickly for ordinary legislative processes. As with other problems requiring government action, it would be best to handle it in a way designed to minimize both the pain caused and the opportunity for power-grabs that expand government control over our economy and society. The revenue-neutral carbon tax advocated by environmental law expert (and Volokh Conspiracy co-blogger) Jonathan Adler, among others, strikes me as a potentially sound approach.

Liberals tempted to use Trumpian emergency powers to fight climate change should remember that Trump is unlikely to be either the last GOP president, or the last dangerous demagogue to get in the White House. In the long run, both left and right would be better off in a world where no one man or woman has the kind of dangerous power to raid the treasury and seize property that Trump now seeks.