Michael Barone: Are Democrats destroying their own credibility?

From Washington Examiner:

You can’t expect a political party to be rigorously intellectually honest on any consistent basis. They’re trying to win elections—and to achieve policy results they genuinely believe to be desirable, and rigorous honesty sometimes has to take the back seat. And anyway, their embarrassed members will argue, the other side does it, and you can’t unilaterally disarm.

That said, it strikes me that the Democratic Party has been taken this to a self-harming extreme. For if the voters catch you stretching the truth and exaggerating the other side’s misdeeds, your credibility will suffer. Even when you state plain truths or make reasonable arguments, many people won’t, or will be reluctant to, believe you.

On what issues are Democrats taking such risks?