There is nothing scientific about this chart. CORRELATION DOES NOT EQUAL CAUSALITY. But, a regression of daily probability for Trump as the Republican nominee and the Democratic nominee winning the general election is highly statistically significant. The intercept is 58 and the coefficient is 0.11. What that means is that if you assume the Democratic nominee has about 58% likelihood to win when Trump has 0% to win and the Democratic nominee is 0.11% more likely to win for every 1% more likely he is to win the nomination that day. Again, there are lot of factors at play in this and I am not implying anything more than there a strong correlation between Trump's probability of winning the nomination and the Democratic candidate winning the general election.