For the umpteen articles calling McCutcheon the sequel to Citizens United, that case was only mentioned once in this colloquy with Justice Kagan:

JUSTICE KAGAN: But the money — the money goes to a single party. And indeed, I could make this even worse. I could say, let’s say the Speaker of the House or the Majority Leader of the House solicits this money from particular people. So solicits somebody to ante up his $3.6 million. And then, you know, Justice Kennedy said in McConnell the making of a solicited gift is a quid both to the recipient of the money and to the one who solicits the payment. So the Speaker, the Majority Leader, can solicit $3.6 million to all the party members and you’re telling me there’s just no special influence that goes along with that?

MR. BURCHFIELD: Well, we know from the Citizens United decision, Your Honor, that gratitude and influence are not considered to be quid pro quo corruption. So I think that’s what you’re talking about. That is not the sort of corruption that would sustain this limit, especially in light of the severe restrictions on speech and association that it imposes as the political parties compete against each other and as they — and as — as the candidates have to compete against each other.

Quid pro quo corruption was referenced only a few other times.

Solicitor General Verrilli picked up on Kagan’s hypo about $3.6 million:

But there is a more fundamental problem here. It’s a problem analogous to the one that was at issue with soft money in McConnell, which is the very fact of delivering the $3.6 million check to the whoever it is, the Speaker of the House, the Senate Majority Leader, whoever it is who solicits that check, the very fact of delivering that check creates the inherent opportunity for quid pro quo corruption, exactly the kind of risk that the Court identified in Buckley, wholly apart from where that money goes after it’s delivered.

And later by Verrilli:

GENERAL VERRILLI: Well, I don’t — with all due respect, Justice Scalia, I don’t think we do. The parties still raise and spend very substantial amounts of money, and so I don’t think that — that we know. But beyond that, what — the Congress has made a determination that there is a real risk of quid pro quo corruption and the appearance of quid pro quo corruption here, and has regulated with respect to that risk, and Congress is of course free to take this into consideration.