Other than Donald Trump in 2016, who declared he would mostly personally fund his 2016 campaign, most presidential candidates use fundraising as their main means of funding their presidential campaign. With this in mind, fundraising can be an indicator of which candidates people are truly behind. I used Datawrapper to take a look and compare the numbers for the candidates of the upcoming 2020 election. Keep in mind these numbers are true for the time period of 2017 until January 2020.
Heres a link to the chart on Datawrapper: https://datawrapper.dwcdn.net/9DksD/1/
Myles' Data Journalism Blog 