I don't think there is an effect to the altcoin after bitcoin halving in 2020, but maybe the altcoin can get down for a while until bitcoin can reach the very highest price. Every possibility can happen in that year since we don't know the truth but one thing that we can hope that bitcoin price will be at the highest rate in the future.

Maybe some altcoin will be down, and the other altcoin could still increase even if bitcoin price increases. I think the altcoin which can rise so high will be the altcoin who can survive in this bear market so they will have a big chance to recover their price after it's in the low price for a long time.

But we can hope that after bitcoin get a pump so high, it is the time for an altcoin to get pump too and gladly, we have so many potential altcoins that can increase in anytime. So you might get prepared for the next pump that will come to the altcoin.