A precedent has not already been set because all the evidence we have is that Obama was born the the USA, and is not foreign born like Ted Cruz. A statutory precedent would be created by the election of Ted Cruz.
Seriously, I do not think it would get that far. The Democrat party would sue in Congress to nullify a Cruz election and it would be upheld. Yet, even before that, a Cruz nominee would face so many vehement attacks from Liberal Democrats through the campaign after the convention that the general election would be a fruitless joke.
I totally agree with you about the elder Obama being a criminal refugee of the bloody Mau Mau uprising. I read the novel, "Something of Value" (1955) when I was just a kid. The initiations and mutilation descriptions were horrifying. Can you imagine what they thought in Great Britain when they had to entertain the son of a vile murderous creature like Obama's father?
Ignoring heinous crimes does not mean a precedent has been set.
From my profile page:
“In keeping silent about evil, in burying it so deep within us that no sign of it appears on the surface, we are implanting it, and it will rise up a thousand fold in the future. When we neither punish nor reproach evildoers, we are not simply protecting their trivial old age, we are thereby ripping the foundations of justice from beneath new generations.”
Aleksandr I. Solzhenitsyn, The Gulag Archipelago 1918-1956