How does a year like 2020 come to an end for investors?

With one of the top economies cleaving off from the largest free trading bloc, of course.

Brexit is here. Sure, the UK formally left the European Union 11 months ago, but this year was governed by a transition agreement that kept the single market trading rules between Britain and the EU in place. That deal is due to expire on Thursday with the end of 2020.

It has been almost four years since UK voters decided to split from the continental trade pact. The intervening time has been spent trying to figure out how to extract the world’s sixth largest economy from 27 other countries without sending people, companies and markets into turmoil. Travel rules, tariffs, even mobile phone roaming charges will change as a result of Brexit.

Since the 2016 vote, the economic barometer of the effect of Brexit has been warning of job losses and recession in the UK. COVID-19 brought all that and more across the globe. However, the pandemic will end. The split between the UK and EU with no trading deal could be worse in the long-term than the coronavirus, according to a warning from the head of the Bank of England last month.

Brexit is more than a distant sideshow for American investors. The uncertain outcome, even if there is a late deal, casts a shadow over hopes for a traditional Santa Claus rally in the U.S. stock market between Christmas and New Year’s. And it may cool the risk appetite necessary to fuel further market rallies.

Markets and investors have shown remarkable resiliency in 2020.

In a year of unprecedented uncertainties, what’s one more?

Financial journalist Tom Hudson hosts “The Sunshine Economy” on WLRN-FM in Miami, where he is the vice president of news. He is the former co-anchor and managing editor of “Nightly Business Report” on public television. Follow him on Twitter @HudsonsView.