Vice President Kamala Harris has to take fact-checking seriously when she goes toe-to-toe with former President Donald Trump on the debate stage Tuesday night. That’s according to former acting solicitor general and legal expert Neal Katyal, who talked to MSNBC host Jen Psaki on Monday night. And just as important, he argued: Harris cannot ignore it if the moderators let Trump slide on key issues. “People know you as a Supreme Court expert, of course, and one of their favorite legal eagles,” said Psaki, a former White House press secretary. “But you were also a champion debater, people should …