'I'm still trying to figure out what covfefe is': MSNBC pundit cautions Trump against 'mental fitness' arguments

President Donald Trump attacked former Vice President Joe Biden over the weekend, challenging his "mental fitness" for the presidency after typical gaffes Biden is known for.

As stand-in MSNBC host Chris Jansing noted, there is a considerable difference between Biden's misstatements or language flubs, and Trump's over 12,000 lies to the American people. The numbers are getting worse as well, she pointed out. Trump initially had an average of 13 lies each day, but as of April, that's increased to an average of 20 lies per day.

"So, it's getting worse," Jansing said.

Democratic strategist Joel Payne unleashed on Trump, saying he's hardly one to question Biden.

"One of the things I will not stand for is Donald Trump talking about anyone's mental fitness to be president," Payne said. "That is laughable. That should be rejected outright. I'm still trying to figure out what the word covfefe is. So, Donald Trump has no standing to question anyone's mental fitness to be president."

Reuters reporter Jeff Mason explained that Trump's supporters either already know that he's a liar or they are willing to conform to Trump's preferred reality.

Biden once joked that the good news about his gaffes is that Americans can be confident that he'll never lie to them.

"And when the president of the United States is the most prolific liar in American political history (he just passed 12,000 false or misleading claims) and is waging a reelection campaign based on racism and fear, the idea that 'gaffes' are an important campaign issue is particularly offensive," Paul Waldman wrote in Monday's Washington Post.

Watch the full discussion below: