Many people have been saying that young voters are going to shift the United States to the left politically. There are a handful of questions on this site about this topic with low propensity young voters generally having more progressive attitudes.

I read online in the Pew Research Center that Democrats in the House won the demographic group that I am asking about by 35% in 2018. But the same Pew study (don't have the link but it shouldn’t be too difficult to find) showed that Biden and Clinton won young voters by only about 20%.

I saw the same sort of story happened in the Georgia runoffs for the Senate vs the Presidential ticket.

Why does there seem to be some sort of drop-off with young voters support of Republicans that accompanies lower turnout elections?