On Wednesday, the House voted to pass a sweeping tax bill, leaving it just one step away from becoming law; all that's left is for President Trump to sign it, which he's vowed to do. Now, critics of the bill will be turning their attention to the question of whether the GOP's tax bill can be repealed.
In short, the answer is yes — with some pretty big caveats. Like any piece of legislation, it can be repealed if the opposing party takes power, passes a new bill through the Congress, and has it signed by the president. That's what Republicans tried, unsuccessfully, to achieve this past year with the Affordable Care Act, after it gained control over Congress and the White House in January.
Of course, to have a shot at repealing the sweeping tax overhaul, Democrats would need to seize both houses of Congress in 2020. It's a tall order even then — as we've seen with the GOP's Obamacare repeal efforts — but by no means impossible.
But in addition to taking control of Congress, Democrats would also need to defeat Trump in his 2020 reelection bid (or, in the event he doesn't run for reelection, whoever the Republican nominee is). Just as former President Barack Obama served as a backstop against repeal of the ACA for years, virtually any Republican president would use veto power to keep the massive upper-class and corporate tax cuts that just passed in effect.
Now, a two-thirds majority could override such a presidential veto in theory; but that's such a steep mountain to climb that a repeal of the GOP tax bill would almost certainly demand full Democratic control of the government —something that hasn't happened since 2010.
It's also worth noting that any piece of legislation which could be conceivably portrayed as a tax increase might be difficult for the Democrats to rally behind politically, which is the more fraught part of the question. In the past, due to the political forces at play ― and perhaps because both parties are awash in corporate money, even though the Democratic Party has been better at advancing the interests of the middle and lower classes ― the Democrats haven't always been good at repealing regressive tax cuts.
The most memorable recent example was when the Democratic Congress under Barack Obama allowed the bulk of the tax cuts implemented by former president George W. Bush, which helped destroy a budget surplus left over from his predecessor, to be extended in 2010, and later made permanent in 2013.
Obama was facing a challenging situation when he initially extended the cuts, as the GOP was effectively leveraging the specter of a tax increase on the middle class to secure ongoing cuts for the rich. But all the same, his decision to give in on the Bush tax cuts drew sharp criticism from members of his own party at the time, and agonized the progressive grassroots.
Basically, that kind of political moment would be the final challenge in undoing the GOP tax plan: how do Democrats choose to articulate their argument against it? How does the public feel about it? And how much political will there will be to get it done? As it stands now, the prevailing political winds are very much in favor of the Democrats making big gains in 2018, but this part of the problem could boil down not just to how much power the Democratic Party has as a whole, but how relatively left-wing its membership is by this time four years from now.
Of course, that assumes that all the dominoes fall just perfectly between now and 2020, and that might not be a safe assumption just yet. Whatever happens, however, it's worth remembering that the bill the GOP is about to pass is not invincible. To the contrary, given a couple strong election cycles, and a Democratic base that holds its members and potential candidates to account on the issue, it could eventually happen. But it's at best years away, and there's an awful lot of work to be done before then.