The future of the global liberal order hinges in large part on the direction of populism in the U.S. After all, the U.S. was the chief architect and custodian of the world order over the past 70 years. If the U.S. withdraws its support, then the order is likely to come unstuck. There are signs that the U.S.’s constitutional checks and balances are weathering the storm in spite of the best efforts of Mr. Trump. The real question now is whether the President and the Republican Party can maintain their hold on government after the 2018 midterms.

Notwithstanding the threats to Mr. Trump of ongoing investigations into Russian interference in the U.S. elections, there are signs that he could survive the 2018 midterm elections and maybe win a second term in office. The reasons for this can be traced to the fact that the U.S. economy is doing extremely well today. While Mr. Trump cannot claim all the credit for this, the recent Republican tax cut is likely to be seen as a positive contribution to general prosperity despite its adding to long-term fiscal deficits. The steady move of the Democrats to the left of U.S. voters, and their continued focus on identity politics, is a boon for Trump supporters. What matters are not the tweets, but the state of the economy.

It is no exaggeration to say that the fate of the global liberal order hangs precariously in the balance. If the Democrats can regain their majority in the House in 2018 and go on to win the presidency, then Mr. Trump is likely to go down in history as an unpleasant aberration. But if the Democrats lose in 2018 and Mr. Trump wins the presidency in 2020, then polarization in the U.S. will deepen and the savaging of liberal institutions will likely increase.