Republicans are on the verge of achieving their decades-long goal: an overhaul of the tax code. But the system they have built will not last.

The plan’s instability is partly a result of the process Republican Party leaders chose to make it happen. Reconciliation, which allows escape from the Senate filibuster, means that Republicans did not have to reach across the aisle. Not a single Democrat supported the legislation.

This choice has consequences. For one, the exclusion of Democrats means that there is no buy-in from the minority party that will one day, perhaps soon, be in the majority again. This dynamic is worsened by the fact that the tax legislation pits blue states against red through the limitation of the state and local tax deductions. In the end, Republicans have chosen policies that are more extreme than they would have if they had worked with Democrats.

The deficit-increasing bill that resulted tilts heavily toward the very rich, financing tax cuts on the backs of future generations. These policies not only face the risk of being undone by a future Democratic majority, but also could indeed prove to be so lopsided as to alienate the more centrist of Republicans. Worse, Republicans now aim to take advantage of the instability they’ve created by cutting so-called entitlements like Medicare down the line, burdening the poor and the middle class.

Republicans have chosen a deep, permanent rate cut for corporations while providing only modest and temporary relief for individuals. Most of the provisions benefiting individuals will expire in 2025, which creates uncertainty for taxpayers and sets up undesirable conflicts in the future as people fight to keep them.

This uncertainty means that the 21 percent corporate rate may not last either. Faced with the specter of a higher rate in the future amid a tumultuous political environment, corporations may continue to search for lower tax rates abroad and limit their investment here in the interim.

This isn’t to say that our tax laws should be set in stone. We could, for instance, adjust tax rates based on macroeconomic conditions, giving automatic tax relief during recessions. But arbitrary expiration of tax laws and unnecessary uncertainty because of politics just upsets planning without gaining anything.

The sunset provisions in the bill will create other problems. The threat of expiration will encourage campaign contributions to lawmakers. For examples, we need only look to the 2001 and 2003 Bush tax cuts, which were also temporary. As the end dates on those cuts loomed, special interests and the wealthy engaged lobbyists in a yearslong fight to make the cuts permanent.

Some of the current bill’s most popular cuts will be made permanent from the start, but they might not ever be paid for. Congress tends to contort the budget process so that expiring legislation is not subject to its normal rules.

The tax bill will also prove precarious simply because of poor policy choices. The deduction for pass-through income is policy incoherence at its worst, lacking any justification and favoring certain industries over others. By taxing wage income and business income differently, the bill also opens up a bevy of opportunities for the well advised to game the system, which will cost the government revenue and sow distrust of the tax system, even of government itself.

On the international side, an area badly in need of permanent reforms, Republicans have erected planks that appear to violate World Trade Organization agreements. Eventually the United States is likely to have to repeal major parts of the law or face sanctions. Rather than ending tax maneuvers in which corporations shift money abroad, the international system envisioned by the bill actually loses money. What’s more, the new international system arguably increases incentives for offshoring assets and income. Good luck to businesses that have to do tax planning in such a wobbly system.

In promoting their tax plan, Republicans allude to the famous revenue-neutral Tax Reform Act of 1986 as their role model, describing the new legislation as a comparable crown jewel in achievement. The 1986 act lowered rates on individuals and paid for them by eliminating special tax breaks and tax shelters that had been used by the rich. In stark contrast, the current tax bill eliminates few tax breaks while opening up a new world of shelters.

The better comparison to the current bill is the enormous tax cut of 1981, which, its proponents said, was going to pay for itself with economic growth. Like this legislation, the 1981 law was a huge tax cut for businesses and the wealthy. The predicted economic growth did not materialize, and the deficit grew instead.

In an attempt to rein in the deficit, Congress had to reverse the 1981 cuts and raise taxes a year later and then again in 1983 and 1984. A similar fate awaits the current bill when this legislation also does not end up paying for itself.

Republicans could have chosen to work with Democrats to enact more lasting, balanced and thoughtful changes to the tax system. They didn’t, and now they will have to live with the consequences. Their victory on taxes is likely to prove fleeting. If so, maybe then they will be ready for real reform.