O que significa stepped into that vacuum ?

See a translation

Lynch’s meeting in June with Bill Clinton on a tarmac in Phoenix led to a crisis in leadership at the department over how to handle the Clinton email investigation. Rather than formally recuse herself, Lynch left ambiguous who would be making final decisions on issues regarding Hillary Clinton.

Into that vacuum stepped Comey, an FBI director who prides himself on having a finely tuned moral compass that allows him to rise above politics. Weeks before the letter, Comey had advised against the Obama administration public statement admonishing Russia for the Democratic Party hacks, arguing it would make the administration appear partisan too close to the election. But to him, the Clinton email investigation was different.