Meanwhile, comparison...
Romney says 47% of Americans are just freeloading on the government. They pay no tax.
Clinton says half of Trump's supporters are deplorable. They are racists, sexists, Islamophobic, or xenophobic. She almost immediately said "half" was a mistake, but that Trump's supporters do include some amount of these deplorables and Trump loves them.
So, first, even if we go with the original "half of Trump's supporters" this is not anywhere near the same breadth of brush as Romney's condemnation of basically everyone who was voting against him.
Second, Romney's premise was false to begin with in that these people don't "pay no tax." There is NO ONE who pays no tax. I live completely off the grid, and I STILL pay tax. Sales tax, gas tax, at the very least in my experience there is literally no way to live in America without paying those. The vast majority of people who pay no income tax, because they are frankly living in poverty, still bear a monstrous burden of payroll tax.
On the other hand, despite years, maybe decades, of protestations by the Republicans, their party has been the safe harbor for racists and all the other deplorables mentioned. They invariably get all indignant and pretend that when that is pointed out it somehow is an accusation that they are ALL racists, because they NEVER want to deal with what being such a safe harbor really means, but to say that these deplorables are backing Trump, almost to the last deplorable man, is seemingly pretty accurate.
The way the Trump campaign is trying to draw this parallel is falling completely flat, for me. I suspect that outside his "I agree with everything he says" base of support that's going to be mostly the case.