When Trump was asked about his refusal to release his tax returns and Clinton cited several returns from the 1970s that showed he didn't pay taxes then, Trump did not retreat. Instead he doubled down, saying, "That makes me smart."
Avoiding taxes, according to Trump, is a virtue, not a vice.
The comment could prove to be extremely damaging if Democrats capitalize on it. According to The Washington Post, a group of undecided voters watching the debate in North Carolina, a vital battleground state, gasped aloud when they heard Trump stay this
. "That's offensive. I pay taxes," one 52-year old civil servant said.
The controversy over his argument brings back memories of the last presidential election. In the middle of the 2012 campaign, Republican Mitt Romney struggled when his opponents -- first, Newt Gingrich in the Republican primaries and then President Obama in the general election -- hammered away at stories about the ways that Bain Capital wreaked havoc on entire communities when their investments did not go well.
They also went after how relatively little Romney paid in income taxes. Romney "paid only 14 percent in taxes -- probably less than you," one of Obama's ads stated.
Those stories, combined with the infamous video clip of Romney complaining about Obama's supporters, who he characterized as being part of the 47% of Americans who are dependent on government, enabled the Democrats to create an image of the Republican nominee as a champion of wealth and privilege. That didn't sit well with many middle class Americans who struggle to get by.
But when he appeared on Bill O'Reilly's show on Tuesday, Trump didn't back down from his taxes comment. Many people, he claimed, say "that's the kind of thinking that I want running this nation."
While some conservatives will praise Trump's well-documented efforts to avoid paying income taxes, his comments might prove to be harmful given the basic premise of his campaign. At the heart of the Trump candidacy has been the promise to help the millions of Americans who are not enjoying the fruits of the revived economy.
Even as all the economic indicators point upward, their daily lives are fraught with uncertainty, insecurity, and constant struggle. Although much of the debate did not go well for Trump, many agree that his most effective moments came when he hammered away in the first half hour on economic issues and baited Clinton into defending free trade agreements.
But the comment about taxes gets to a fundamental weakness in the Trump appeal. At this point there is no "there" there. The actual policies on the economy that the GOP has promoted in recent years don't quite deliver on the promises he is making.
There is little evidence that the Republican agenda of deregulation, supply-side tax cuts, and cutting the social safety net add up to an economic future that is better for most Americans. Trump has been less clear on where he stands with domestic programs, other than Social Security and Medicare (where he broke with Ryan's reform agenda), but his economic policies generally fit
under the Republican tent.
Democrats have gone to great lengths to argue that Republican economic policies are highly regressive and tend to support the kinds of economic forces that have undercut the security of the middle class. When Trump, a wealthy man, boasts that he doesn't pay taxes, he plays right into an image of greed and elitism that can be used to undercut the arguments he is making to working voters in states like Pennsylvania and Ohio.
This is an argument that Clinton needs to emphasize, one that goes beyond the attacks on whether he is competent enough to hold office. The Trump appeal to disaffected Democrats is a two-part mix -- one part anger against immigrants who he incorrectly claims are taking away American jobs, and the second an attack on the economic policies of his opponent.
While the first part of the Trump agenda will be hard for Clinton to combat, given that those animosities are deeply imbedded, the other part can be debated more successfully with undecided voters. She will have to debate his conservative populism if she wants to reverse the kind of poll movement in Trump's direction that we saw over the past month.
The tax comment gets right to the heart of a fundamental problem with the Trump campaign. Conservatism populism does not have a strong policy foundation. Trump claims to be the candidate of average Americans and he claims to be the candidate who will help struggling workers, but there is so much about his background as a businessman and his actual economic policy proposals (which have not been as unorthodox as some claim) that don't support that argument.
There is a reason that Bernie Sanders and Elizabeth Warren, who have both been highly critical of Clinton in the past, are making it clear that they have no doubts about their preference in this general election.
When Trump boasted in the debate that he was proud of not fulfilling one of the most basic obligations of all citizens -- paying their taxes -- particularly as someone who allegedly has so much wealth, he opened up a huge opportunity for Clinton.
In the next few weeks we will see if she runs with this and can avoid getting sucked into a back and forth of character assassination that will become more tempting as Trump and his surrogates unload on her marital history, her emails and the Clinton Foundation. As Bill Clinton's campaign understood in 1992, "It's the economy stupid," and Democrats would do well to remember that lesson.