It's a very interesting quote. To take something literally means to take the literal or exact meaning of what someone says. It is usually used when someone misinterprets what someone else is saying. For example, if someone says "I'm so full I will burst at the seams", they don't mean they will really burst. Someone taking them literally would believe they would really burst when that is not what they meant. It is just an expression to convey how full one feels. I believe the quote means that Trump's supporters did not take him literally but supported his basic stance on most topics. For example, when he said he would build a wall between Mexico and USA, or promised to deport all illegal aliens from the USA, his supporters believed this was meant to convey his hard stance on immigration, not that he really intended to do those things (which would be almost impossible). I hope this is the case with Trump. Knowing how little of politician's promises are actually carried out, I think it is quite a safe assumption. On the other hand, Trump's critics took his words literally and hence not seriously, given the extreme nature of much of what he said.

Trump's supporters did not think his words important, but his critics did. This led his critics to disregard his candidacy, while his supporters did not waver.

"take sth seriously" = take sth. solemnly or thoughtfully in character or manner "take sth literally" = take sth. for its face value, i.e. if somebody claims that he hates immigrants, not to try to search some hidden meaning behind the words