Donald Trump’s cabinet nominees so far reveal a desire to disrupt Washington, and disruption is needed in many places. But as he mulls his choices for Treasury and the economic-policy posts, the question markets will ask is whether he will disrupt the policy mix that was successful in his first term.

The voter election surveys make clear that Mr. Trump won his second term above all else on the economy. Voters rejected the results of Bidenomics, especially inflation and a decline in real incomes. They recalled the strong investment and job market and rising wages across all income levels of the pre-Covid economy. Mr. Trump’s second term success or failure will depend on restoring those results.

That’s the hope behind the market’s bullish initial response to Mr. Trump’s re-election. Investors anticipate a return of animal spirits as the pall of Democratic tax increases and regulatory coercion is lifted. But economic and financial risks remain, and they’ll require careful judgment, not blow-it-all-up rhetoric.

That’s why it’s strange to hear Elon Musk lobby Mr. Trump that the next Treasury secretary shouldn’t be someone who favors “business as usual.” What he means by that isn’t clear beyond favoring one personality over another, and Mr. Musk may not know. Fiscal and monetary policy aren’t his specialty.

One risk ahead is the tax bill that needs to pass next year to extend the 2017 tax reform. With narrow GOP majorities in Congress, that won’t be easy. All the more so because Mr. Trump campaigned on new tax cuts (on tips, overtime, Social Security benefits) that will be impossible to afford unless Republicans want to sign up for an even larger deficit blowout than under President Biden.

Extending the 2017 reform more or less intact might be the best policy. That reform has recouped more tax revenue than the critics and Congressional scorekeepers claimed, and it will continue to do so if the economy keeps growing. But piling on too many tax giveaways that won’t improve the incentive to work and invest could make tax reform difficult to pass and spook the bond markets. The U.S. deficit as a share of GDP in the last fiscal year was 6.4%, which is unheard of in a growing economy without a war or pandemic.

We assume someone has told Mr. Trump that disinflation seems to have stalled. Long bond rates have climbed since the Federal Reserve cut short-term rates by 50 basis points in September. The 10-year Treasury yield is now above 4.4%, while the average 30-year mortgage rate is nearing 7.5%, higher than on Election Day. This means the Fed’s rate-cutting spree may soon have to end, lest inflation make a comeback on Mr. Trump’s watch.

The largest uncertainty is the President’s trade policy. There’s no doubt he will impose tariffs of some kind on Chinese goods and seems determined to impose some broader tariff across all imports. Whatever one thinks of tariffs as a policy tool, they add uncertainty to business investment decisions.

Unlike other policy positions, the Treasury Secretary needs an understanding of financial markets, which nowadays are global. A blowup in the foreign-exchange markets somewhere can affect the U.S. economy, and new financial investments like crypto need careful watching.

Mr. Trump’s first term until Covid was an overall economic success, as his tax reform and deregulation overcame the drag from tariffs. Markets responded well to his victory because they hope for a repeat. But that requires sound policy, not willy-nilly disruption.

— Wall Street Journal