Many economists have analyzed the policy differences Mr. Biden or Mr. Trump will bring to the U.S. economy. Equally important will be the consequences to the economic policies of the losing party. Our two-party system depends upon the competition of ideas. The ability of both parties to eventually appeal to a majority of citizens tempers passions and promotes compromise.

If Mr. Trump wins, the Democratic party will surely resume its debate over far-left versus center-left policies that animated their primary. This has thus far been a healthy debate, building on decades of democratic policy. I have strong disagreements with the Democratic platform, but no one can honestly argue they are not mostly serious and target the concerns of most voters. If defeated, the Democrats are unlikely to make substantive adjustments, viewing defeat as a problem with the messenger, not the message. To his credit, Mr. Biden said so himself.

In contrast, if Mr. Biden wins, the Republicans have two truly extraordinary challenges in re-forming a coherent economic policy. The first lies in conjuring any set of policies from what is today a collection of often contradictory, sometimes transient whims. The second lies in attracting a majority of future voters given the broad electoral challenges that weigh mightily on the party.

For nearly a half century, GOP economic policies coalesced around a broad set of priorities. The party claimed their platform was fiscally prudent, pro-growth, pro-immigration, supportive of free trade, and possessed with a penchant for limited government. The GOP embedded its economics in a broader policy environment that sought to promote American interests abroad. With good reason, the GOP claimed its elected leaders possessed character and competence.

Like the Democrats, the GOP often fell short of their ideals, but they were clear with the framework of who they were and what they wanted to do. Over a half century the GOP held together a coalition with economic policies providing the core domestic policy success. Today that alliance is in shambles, and rebuilding will prove a daunting task.

Mr. Trump's economic policies are neither effective, nor those of the successful GOP coalitions of the past. Only his most forgiving and myopic of supporters would claim he supports the core elements of economic conservatism. The 2019 budget bill was a fiscal calamity, creating deficits that would’ve made the most profligate Democrat blush. Mr. Trump is not only anti-immigration across myriad policies, he inexplicably curtailed the in-migration of the best-educated foreigners. His immigration policies aren’t about economic ascendancy, but something else altogether.

The GOP can claim only transient success on regulatory reform. Lacking the competence to pass legislation, the entirety of the Trump reforms can be erased by a new president. His trade war proved a disaster. China emerges stronger in its wake while the U.S. slipped away from important international institutions that formed a fire-wall against China’s trade practices. By late 2019, the Midwest was effectively in recession because of the Trump trade war. The Tax Cuts and Jobs Act, which I praised in this column, achieved few of its policy goals, undone by trade war follies. This has been an inchoate four years.

The COVID-19 pandemic is now the most consequential executive branch failure in the 244 years of the Republic. It amplified Mr. Trump’s substantial flaws in character and competence. He failed to confront the pandemic and support basic, uncontroversial public health measures. Instead, he lost his nerve over the stock market and lied repeatedly about the risks of the disease.

Along the way, Mr. Trump ruptured the moral judgment of large numbers of his supporters. The indecent obeisance shown by those who proudly shun masks and social distancing ranks alongside the worst impulses of the human experience. For these Americans, the coming months should be a time of repentance and reflection.

The challenge to future GOP leaders is that Mr. Trump soiled nearly every high ideal that held together the conservative movement for a half century. He replaced them with a yawning emptiness. In the midst of a global pandemic and worst economic downturn since the Great Depression, the GOP could not even summon the basic competence to offer a party platform. Instead of appealing to the boundless character and courage of the American people, Mr. Trump and his sycophants ridiculed them for wearing masks. This is a party wholly bereft of ideas.

The future of the GOP coalition is decidedly bleak. A recent Pew poll shows Mr Trump winning only among voters older than 65 and white voters who have not attended college. Ronald Reagan twice won election with a majority of the 18-24 year-old voters, while Mr. Trump is losing them by 3 to 1. I was one of those 18-year-olds who voted for Mr. Reagan in 1980. In this election, Mr. Trump is poised to lose badly among those now 55-64 year-olds who helped sweep Ronald Reagan into office.

In short, Mr. Trump gutted the conservative coalition, retaining popularity only with the most rapidly shrinking segment of future voters. Perhaps worst of all, his repeated winks and nods to the previously torpid morons of the white nationalist movement have poisoned the party. This behavior is so repulsive that many Americans will never again consider the GOP palatable, no matter the strength of their economic platform. In short, if you wish to eradicate a successful political coalition, Mr. Trump provides a comprehensive example. This has serious post-election consequences.

If Mr. Trump wins, his administration faces a Congress with clear and popular policy alternatives with whom he must compromise to pass any legislation. A victorious Mr. Biden faces no such constraint. There are no broadly held, coherent, affirmative ideas in the GOP opposition. If Mr. Biden seeks compromise, it will be on his terms, with an eye towards expanding the Democratic coalition for a generation.