[Belegorn]

I agree. I think Denethor held to the decision the old council made, that only an heir of Meneldil/Anárion who met the criterion [male line of descent, nearly pure Númenórean bloodline] could claim the throne. However, at the same time it would seem to me that many of the other nobles would see it differently and would accept an heir of Isildur. I doubt at this time there would have been Civil War since there were few Dúnedain left anyway in the South Kingdom.