The SC being conservative is the result of a democratic process, not a threat to it.

If Trump wanted to be dictator, why didn't he just do all that stuff in his first term and not worry about reelection in 2020?

Things take time. Erosion of trust and the creation of political apathy in the populace takes time. Also, as has been said, he did try things but was continuously pushed back on by the actual politicians he put in his cabinet. He's also 8 years more elderly and emboldened. His cult of personality has essentially stabilized into an American institution. He's also had an entire administration to place judges and pass legislation that favors his power plays. In general it seems like you're asking, why might it take more than 4 years to topple a democracy, which i think has an obvious answer, democracy doesn't want to be toppled.

Again, I'm not arguing he's gonna go full dictator, but i think it's a lot more likely this time around than last time.