Been reading about the hypothesized Renly/Tyrell conspiracy to replace Cersei with Marg and expose the twincest, and it got me wondering: what was Renly waiting for? It seems like he had all the pieces at hand for a coup, he just needed to get Marg to KL. Was he waiting for better evidence of the twincest? Was Marg not yet old enough? Was he just dithering? Did Jon Arryn's death make him cautious? What do you think? Did the plan ever have a chance? Did he realize LF had an agenda too?
Margaery’s age, at first - she’s sixteen for the bulk of ASoS, at least, meaning that she was quite possibly fourteen in the earliest parts of AGoT. The idea to marry her to Robert was probably floated when she was fourteen-fifteen. Don’t forget, either, that Renly’s twenty-one in AGoT and Loras sixteen. Neither of them are hugely experienced schemers.
And yes, the political situation did stall things. Jon Arryn’s death is not only a political event, but a personal matter for Robert; shoving Margaery at him when he’s trying to actually grieve for someone might come across a bit tacky and put Robert off. Likewise, interrupting Robert’s “I got my BFF back!” high might also go poorly. The royal progress to Winterfell and the Tourney of the Hand are both disruptive to court business as normal. Ned himself had to be factored in in terms of replacing Cersei. Then the Stark-Lannister feud kicked into a higher gear.
Until Renly had the marriage to Margaery ready to go, right then, Robert’s cooperation guaranteed, he didn’t have the pieces he needed. There wasn’t a great window for him to bring a sufficiently grown-up Margaery to court in AGoT, and so the plan ended up not happening.