unassailable

Victory gives them an unassailable 3-0 lead in the five-match series, with two matches left to be played.

It wasn't too long ago - in the 1970s and 1980s - that Republicans were viewed as having a unassailable lock on the presidency because they consistently won a majority in enough states to prevail in the electoral college.

At that stage in the summer, electorally, Trump looked unassailable.

As part of her predecessor’s legacy, she enjoys an almost unprecedented level of support with the ruling party in an unassailable position across the country.

On the merits, the cases for both defamation and emotional distress are strong—perhaps unassailable.