President Trump said the U.S. would impose 100 percent secondary tariffs on countries that trade with Russia if Moscow does not agree to a ceasefire in Ukraine in the next 50 days.
The EU is not trying to “buy up Ukraine at a discount”, they are pushing for Ukrainian EU membership, which would be mutually beneficial. On the one hand, the EU would gain massive strategic food production and a large experienced military, and further buffer area towards Russia.
EU tried to get its own minerals deal with Ukraine in the wake of Trump demands.
Also Ukraine joining the EU would not make a "buffer", unless you would argue in terms of first and second class EU countries, with Ukraine being designated to become a second class one. Ukraine currently is the "buffer" as it is aligned with the EU, but not part of it, so the EU does not bear the same responsibilities towards Ukraine as to other EU members.