The judge, prosecution and defense get to vet each juror by asking them about their beliefs and biases. They can reject jurors if they believe the juror is unable to hear a case without being impartial. Jurors (often) won't be told the details of the case they'll be hearing while they're being vetted, only the basic details (e.g. defendant is a white male accused of murdering another white male).

In extremely high profile cases like the ones featuring Donald Trump, courts focus on selecting jurors who can remain fair and impartial despite their knowledge of the case or their own personal opinions. They'll go through extensive vetting which can include written questionnaires, interviews, oral questioning about their media consumption, their political beliefs and potential biases, and so on.