Recusal in a situation like this is always a question of judgement. The general rule is that a person who has an interest in the outcome, should not be allowed to pick their own judge, and (in the case of a judge) should not be allowed to decide the case. One who has an interest may or may not be impartial, but in the interest of preserving public trust in "the system," (as well as giving the parties an unbiased shake) that person should step aside from this one decision.
Much as I detest the ABA, it has a point here. Cruz is potentially THE party in the case!
Under the notion, all senators should recuse themselves because any of them might end up running for president (such as Garfield in 1880).
It regards a judge of the people, not a judge to serve one president. Or I might be wrong. I have been wrong before.
Just because someone might, maybe, sometime in one of many possible futures bring such an action would be no reason for Cruz to abdicate his Senatorial responsibility to vote on such a nominee.
As it stands there is no conflict of interest, because no such action has been brought in any court, much less before the SCOTUS.
If the standard for recusal was set at the possibility that a member of The Senate might end up in an action before the court in the future, then neither the POTUS nor the Senate could have any say in the matter. Any person in the US has the potential to be a party in a case before the Court, therefore none of them could vote, and even an appointment would be a possible conflict someday, some how, sometime.
Obviously, the standard would have to be, at the very least, one in which there was a case pending before the bench.
One would think Harvard Law Schooled lawyer Ted would be a bit more grounded in the law... jurisprudence is not his strong suit.
Also technically we vote for state electors, not the party headliners whose names appear on the presidential election ballot. The USSC cannot interfere with the constitutional mechanism used to elect the president as it is a violation of the separation of powers.
We would probably agree that a liberal court would more likely find both O and Cruz to be NBC's. It is also likely candidate Sen. Cruz would vote against a liberal nominee and be, in essence, voting against his interest.
Likewise, if he is the successful candidate one wonders if he would nominate a conservative who understood the history and context in which the founders used the term NBC?