Mark Shields:

A couple of numbers, Judy — 537 votes, that was 2000. That was Florida. That's what Al Gore lost to George Bush and lost the White House.

Democrats have not — why did he lose it? Well, one Democratic explanation is, there were 97,498 votes cast in Florida that year for Ralph Nader. If Ralph Nader had not been in the race, very little question that Al Gore would have carried Florida, would have been president of the United States.

So third parties have been spoilers, rather than change agents, for most — in American politics.

And, at the same time, I agree with David that there was no — there's no constituency, other than a couple of editorialists and very thoughtful journalists for fiscal responsibility and cultural liberalism, and that it's a — you're talking about one-third of 1 percent.

Donald Trump depends on one thing. He's the only president in the history of the country that, every day of his presidency, now some 742, he has never had a positive day of polling, either personally or professionally. He needs a third-party candidate. He needs probably a third-party and a fourth-party again, so his 41 or 42 percent will get him there.

And I think that's what you got in Schultz, who is kind of a — you're coming in to be a spoiler. And Democrats kind of understood that the important thing is to beat Donald Trump. At the same time, Democrats this week are spending time arguing about who can be the most leftist activist in party.

The reality is, since 1990, the income, the household income of the top 1 percent has doubled in the United States, has doubled. That's the top 1 percent. Among the median income, household income in the United States, it's increased — increased by 6 percent.

So the disparity in wealth is there. And the ability to pay is — I think the value that has embraced — Democrats have embraced in taxation. But, again, what you don't want to do is give Donald Trump a chance to make you the issue running against him.

You want 2020 to be a referendum on Donald Trump, up or down on Donald Trump, not on some Democratic internal fight over issues.