Voters in Northern Ireland will elect a new assembly next week.
Polls suggest that Sinn Fein could become the largest individual party.
That would mean that for the first time Northern Ireland could be led by a Republican first minister.
But under the power-sharing rules, that can only happen if the Democratic Unionist Party agrees to take the post of deputy first minister.
That is an unimaginable prospect for some unionists, even though the two posts have equal power.