We don’t know what Harris would or wouldn’t have done. But we know that what Trump is doing is not going to end up well for Ukraine.
Dealing directly with Russia as if it was up to the US to decide for everyone else isn’t just callous, it’s extremely dangerous.
So yeah up until now Trump has done _nothing_ to stop this war. He's really only proved to all the US' supposed allies, that the US is not trustworthy. At this point, Trump should just shut up and stop pretending like he's trying to reach some peace agreement. He should just stop sending funds to Ukraine as he obviously wants to do and just leave the discussion because he's really no longer relevant.
However, if by "genociding Ukrainian people" you mean eradicating the population of Ukraine that considers itself distinct from Russia, Trump could conceivably stop the war by letting Russia hold onto territories it owns, while having the rest of Ukraine as a protectorate of various European powers that may eventually bring it into the EU.
This might result in a populatin exchange as Russian speakers get sent to the Russian-held parts of Ukraine and vice-versa. This would not be good but it would not be a genocide either. You can also look at the Indian partition for an example of how this could go horribly wrong.
Russia does not care the slightest about the territory, it is purely a war about ideology and influence.
The only acceptable outcome from a Russian perspective is a Russia aligned government in Kiev, or a peace deal where they will rebuild their army and end up stronger than Ukraine followed by restarting the war.
Sides, Russia's got nukes. It's nuke's are the whole reason why the US and Europe has been reluctant to intervene. If, in this scenario, Russia invades Ukraine again and then simple say that it will launch it's warheads at any nation that attempts to intervene, what then?
So, only ethnically cleanse the areas they already started on. Genocide in a limited and specific way is still genocde.