Here is a McClatchy article on this general topic. How saying something at the right time, on the right topic, works to Trump's benefit, as opposed to saying nothing --
"Democrats decided 16 months before the 2018 election how they would start winning races again. Gathered in a small Virginia town on a sweltering July day, Chuck Schumer, Nancy Pelosi and their lieutenants laid out a “Better Deal" agenda focused on middle-class jobs and higher wages — a vow, they said, that their party would never again waver from a laser-like focus on the economy.
Donald Trump makes some promises difficult to keep.
Just days later, the president declared on Twitter that transgender men and women were banned from the military. His action drew a swift rebuke from Democrats, who rose in unison to denounce the president over the newest front in a cultural — not economic — fight.
The pattern would repeat itself through the summer and into the fall. Whether it was his response to the Charlottesville white nationalist march or his condemnation of NFL players who knelt during the anthem to protest police brutality, Trump forced Democrats onto the battlefield of his choosing.
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“As much as I’m appalled by the daily actions from the Oval Office, I have to admire the president’s ability to keep us talking about anything other than jobs and economic well-being,” said Democratic Rep. Jim Himes of Connecticut. “If we keep falling for that, we will pay a huge political cost.”
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To many Democrats, Hillary Clinton’s campaign was too fixated on Trump’s moral failings and obsessed with the Republicans’ litany of rhetorical offenses. But some worry that a singular focus on jobs is simply too hard to maintain. Trump is good at picking out divisive cultural issues and mainstreaming them. And while Democrats doubt his provocations are part of a grand strategy, they say he has a rare instinct for choosing fights that will thrill his base. (Said Ohio Democratic Party Chair David Pepper, “When he’s engaging in divisive culture war fights, that’s when he seems the happiest.”)
A month after the “Better Deal” rollout, Trump leaned into his most controversial fight yet, saying there was “blame on both sides” between white nationalists who rallied in Charlottesville and the people who showed up to protest hate groups.
In a case like that, Democrats felt morally compelled to respond....."
http://www.mcclatchydc.com/news/politics-government/article182495486.html