Donald Trump’s renewed call for Supreme Court Justice Ruth Bader Ginsburg to resign over her critical comments on his presidential bid is really just a suggestion. Why?

Like 'em or not, Supreme Court justices are appointed for life.

Impeachment by Congress is the only legal avenue that exists for punishing or removing a Supreme Court justice -- a historically rare option that’s been tried, but has never succeeded.

The congressional bar for impeachment starts relatively low -- that is, the House only needs a simple majority to vote for impeachment proceedings to begin; but the bar is raised fairly high in the Senate, where a two-thirds majority is needed to convict.

The last – and only – time this happened was in 1804, when the House voted to impeach Justice Samuel Chase. He was accused of a range of offenses concerning his conduct on the bench – but the Senate voted to acquit in 1805, and Chase stayed on the bench.

One other justice, Abe Fortas, resigned in 1969 amid threat of impeachment over an ethics controversy.

Sen. Ted Cruz, R-Texas, told Fox News last year that the Senate can barely muster 50 votes, let alone 67, to oust a Supreme Court justice. He called instead for judicial retention elections every eight years – something that does not currently exist.