By Marc A. Thiessen

How can a president as successful as Donald Trump be so unpopular?

Fueled by his historic tax reform and an unprecedented regulatory rollback, the economy grew by 4.1 percent in the second quarter. The unemployment rate is just 3.9 percent — near the lowest it has been in nearly two decades — and the New York Times reports, “Job growth is on a record streak [and] American factories … are hiring at their fastest rate in two decades.” African American and Hispanic unemployment rates are at near record lows. And the unemployment rate for women is the lowest it has been since 1953.

Virtually everyone is doing better thanks to the Trump economic boom. And yet the president’s approval rating is stuck at 42 percent. Even worse, his disapproval rating has risen 11 points since his inauguration. When asked if Trump is doing an “excellent,” “pretty good,” “fair” or “poor” job as president, a stunning 45 percent say Trump is doing a “poor” job.

Part of his disapproval is driven by the intensity of the Democratic “resistance,” and the ongoing investigation by special counsel Robert Mueller has certainly taken its toll. Others are put off by his tweetstorms and the chaotic nature of an administration that produces self-inflicted wounds such as family separations at the border.

But ultimately, what makes it impossible for many Americans who approve of Trump’s policies to also approve of Trump’s presidency is his failure to definitively reject and ostracize the bigots who inhabit the fever swamps of the alt-right. A year after Charlottesville, Trump has still not explicitly condemned them. “Riots in Charlottesville a year ago resulted in senseless death and division,” Trump tweeted Saturday morning. “We must come together as a nation. I condemn all types of racism and acts of violence. Peace to ALL Americans!”

Sorry, that’s not good enough. Not all types of racists were marching in his name in Charlottesville. Not all types of racists held a rally after his election in which they shouted “Hail Trump!” Not all types of racists continue to claim to be a part of Trump’s coalition.

The fact that the Unite the Right rally in front of the White House on Sunday fizzled does not let Trump off the hook. His defenders will argue that there are always protesters outside the White House, and none of his Republican or Democratic predecessors was expected to comment on them. Why should Trump have to do so? The answer is simple: because the ethno-nationalists of the alt-right have embraced him, and Trump has failed to make clear that he does not accept their support.

This is not hard. After some white nationalists praised a recent monologue she delivered, Fox News host Laura Ingraham went on the air and blasted them, declaring to “all white nationalists … you don’t represent my views, and you are antithetical to the beliefs I hold dear.”

Why can’t Trump bring himself to say the same thing?

Trump’s failure to reject the bigots of the alt-right not only tars his presidency, it also tars his supporters. The overwhelming majority of people who voted for Trump are not racists. They are good, decent, patriotic Americans who were sick and tired of being ignored by the political establishments of both parties in Washington. They had legitimate grievances that were not being addressed, from the opioid crisis to an economy that was not giving them the chance to work and pursue lives of dignity.

Trump’s election finally gave them a voice. But his failure to condemn the alt-right allows his critics to dismiss his supporters’ valid concerns and lump them in with the tiny minority of bigots who have embraced the president.

His failure to condemn the alt-right has also prevented him from expanding his support beyond his core supporters. With his record, he should be winning over millions of Americans who did not vote for him in 2016 but whose circumstances have markedly improved under his presidency. Instead, his support is stagnant and his disapproval is growing. He would gain far more supporters by rejecting alt-right bigots than he would lose.

The fact is many Americans support Trump’s policies — from his outstanding Supreme Court picks to his bold economic reforms — but don’t support him for one simple reason: They don’t want to be associated with a man who seems to have so much trouble telling the white nationalists of the alt-right that they don’t represent his views and are antithetical to the beliefs he holds dear.

Follow Marc A. Thiessen on Twitter @marcthiessen.