It is meaningless to compare Trump's fundraising to that of the Dem. candidates at this time but not for that reason. Whichever Dem wins the nomination will almost certainly start the General Election campaign with a 'war chest' at or near $0, while Trump will likely have the full amount raised to that point.
Glad to report you are off base there. The true state of affairs is the the democrats are involved in a primary election, behaving and spending like it. Trump is running a reelection campaign and has been for over a year.
Since May 2018 -- when Facebook and Google began releasing advertising data -- the Trump campaign and the Trump Make America Great Again Committee have spent more than $33 million across the two platforms. By comparison, the Trump campaign has spent more than $7.5 million on traditional TV advertising during that period, according to data from Kantar Media/CMAG.
The digital ads focus heavily on list-building and fundraising.
"The difference between [Obama's] first election and his reelection -- he grew his list by about 50, 55%. We're going to grow ours about 300%. You know, maybe even 400%. We're already at 150% growth with our list size," Parscale told Fox.
https://www.cnn.com/2019/11/07/politics/trump-digital-advertising-spending/index.html