The 2016 presidential campaign has made Donald Trump a hero to millions of Americans. It has also exposed him as a serial liar, his critics say.

People tend to believe that all candidates for public office lie. But lawyers for the plaintiffs in the upcoming Trump University civil trial argue that Trump has taken lying to a new level, Reuters reports. The attorneys say they therefore should be allowed to bring up the Republican nominee's campaign talk in court to impeach his credibility as a witness.

Trump's lawyers insisted in a court motion last month that any and all statements by their client on the campaign trail should be excluded from the case "because they could unfairly prejudice the jury."

The plaintiffs' attorneys have countered that Trump's statements as a candidate show the real man -- one who constantly spews out a "melange of misrepresentations, falsehoods and flip-flops." They added that Trump's motion for exclusion is ridiculously broad, seeing as the campaign has led him to address past business dealings, his tax returns and other behavior relevant to the fraud case.

"In the course of the campaign," they wrote, "news organizations have collected and publicized practically every known Trump falsehood over the years, bringing all such statements within the gambit of Trump's motion."

Several former Trump University students are suing Trump for fraud over his now-defunct series of real-estate seminars. New York Attorney General Eric Schneiderman believes the seminars were "a classic bait-and-switch scheme." So does former Trump U. salesman Ronald Schnackenberg.

"Based upon my personal experience and employment," Schnackenberg testified, "I believe that Trump University was a fraudulent scheme, and that it preyed upon the elderly and uneducated to separate them from their money."

Trump, whose top campaign theme has been his call to build a wall along the southern border to keep out illegal immigrants, raised a ruckus in May by declaring that the case's judge, Gonzalo Curiel, could not be impartial because he is "a hater of Donald Trump" and "Mexican."

Curiel, a U.S. District judge who prosecuted Mexican drug smugglers during his time as a federal prosecutor, was born in Indiana.

-- Douglas Perry