The states and the federal government are separate sovereigns. The feds can't and won't take the case away from the state; instead, the prosecutions will continue on those two separate tracks. Minnesota will prosecute him for murder and attempted murder and whatever other charges are appropriate; in the meantime the feds have apparently found a basis in the evidence uncovered so far to confer federal jurisdiction - apparently based on the use of firearms to commit another federal crime, maybe something involving interstate travel. Whatever that is, the two prosecutions are independent. Double jeopardy won't attach because of the dual sovereignty principle, meaning that federal murder and state murder are considered separate offenses and he can be prosecuted for both.
The state charges would appear to be a slam dunk; Boelter is virtually certain to be convicted if he doesn't plead guilty first. The sentence is likely to be life without parole since MN doesn't have the death penalty. He cannot be pardoned on those state charges. The fed is seeking the death penalty, for which Trump has a huge hard-on. Since Trump's pardons are based on bribery and Boelter doesn't seem to be in any position to offer a bribe, a pardon is unlikely, even if it would trigger the libs. Trump doesn't care about that; he just wants to be able to grift off the pardon power. A pardon or a commutation would save Boelter from the death penalty and that's it. Given the evidence so far I expect what will happen is that Boelter will plead guilty to everything to avoid the death penalty and accept LWOP, and that will be the end of it.