CNN uncovered a letter dated February 12, 2016, in which Sens. Rob Portman (R-OH), Ron Johnson (R-WI), and Mark Kirk (R-IL), along with several Democratic senators, called for Ukraine’s then-president to “press ahead with urgent reforms to the Prosecutor General’s office and judiciary.” Four days later, Shokin resigned (although he didn’t officially leave until the following month when Ukraine’s Parliament voted him out).
In other words, both Republicans and Democrats in the US — and many European nations — wanted Shokin gone for failing to clamp down on graft.
The letter is a major blow to Trump’s argument that Biden somehow went rogue and tried to get Shokin fired to protect his son. Biden himself has been incredibly consistent on this point, saying he legitimately pushed for the prosecutor’s ouster with international backing and that he never spoke to his son about his Ukraine work.