Denna exakta fråga behandlas mycket tydligt i böckerna. Ren berättar Catelyn exakt vad grunden för hans påstående är ( En Clash of Kings , s.319):
"It would seem that you are the one who has forgotten Stannis," Catelyn said, more sharply than she'd intended.
"His claim, you mean?" Renly laughed. "Let us be blunt, my lady. Stannis would make an appalling king. Nor is he like to become one. Men respect Stannis, even fear him, but precious few have ever loved him."
"He is still your elder brother. If either of you can be said to have a claim to the Iron Throne, it must be Lord Stannis."
Renly shrugged. "Tell me, what right did my brother Robert ever have to the Iron Throne?" He did not wait for an answer. "Oh, there was talk of the blood ties between Baratheon and Targaryen, of weddings a hundred years past, of second sons and elder daughters. No one but the maesters care about any of it. Robert won the throne with his warhammer." He swept a hand across the campfires that burned from horizon to horizon. "Well, there is my claim, as good as Robert's ever was."
Moogles svar är bra, men inget slår ett canoncitationstecken! :-D