The most-watched figure in Slovakia’s elections on Saturday is a populist former prime minister who was forced out of office five years ago amid public outrage over a journalist’s slaying, but who is now within reach of leading the country once again.

A return to power for Robert Fico, a brash strongman with sympathies toward Moscow, could break a key link in the Western military alliance supporting Ukraine. That has put outsize international focus on the vote in a country of just 5.5 million people.