Fox News host Lara Trump joins ‘Fox & Friends’ to preview the upcoming testimony from former President Joe Biden’s chief of staff, who is set to appear in the probe into Biden’s mental fitness while in office. #foxnews #news #us #biden #breakingnews #washington #whitehouse #usa #joebiden #investigation #health #media #new Subscribe to Fox News! https://bit.ly/2vBUvAS  Watch more Fox News Video: http://video.foxnews.com  Watch Fox News Channel Live: http://www.foxnewsgo.com/ FOX News Channel (