They’ve been out to get Trump since the beginning and nothing stuck. They are out of bullets. The notion that they are holding back until Trump gets in a position to win is ludicrous. If he is the nominee, it is too late. They would have taken him out a long time ago if they could.
Why would the Democrats try to destroy Trump before he is the nominee? Why not hold onto damaging information and unload when Trump is the nominee and the Republicans would have little or no chance to respond or change courses? The Democrats have been masters of that eleventh hour surprise. Instead of being complete, the vetting process on Trump is just now starting.
How can you assert that they are out of bullets? Do you know everything that there is to know about Trump? Do you know all his business dealings? Do you know all his personal information? Do you know all the ways he has "worked the system" to get what he wanted? It has only been in the past few weeks that the Democrat establishment has seemed to realize that Trump might be the Republican nominee. Opposition research on Trump by the Democrats has probably only recently started in earnest.