Earlier quoted context omitted.
You're referring to the process of finalizing a treaty. That would be conceptually similar to "executing" an agreement between parties—the most important step that makes it legally binding! But "reaching a deal" and "executing the agreement" are often different steps. When we have discussions with a client, and we negotiate on the terms we can reach an agreement on the negotiation before we actually execute the contr…
Your analogy is flawed because you seem to be assuming that the people with execution authority are the ones who reached an agreement in principle. You’d expect them to succeed in papering it up. That’s not the case here. The agreement in principle was reached by someone who has no power to do anything with regards to corporate taxes. Congress sets U.S. tax law and agrees to treaties. To do that, you need 60% or 66%…
"reached a deal" doesn't mean the deal absolutely 100% will be implemented. It means, the referenced parties have reached an agreement to something.
In this case, the leaders of the G7 countries have reached an agreement among themselves to have a minimum corporate tax rate. Note that the United States has no obligation according to this deal—only Joe Biden has agreed the deal. And Joe Biden has no legal obligation under the deal, he merely has a reputational one.
Since the agreed minimum corporate tax rate is 15%, and the United States corporate tax rate is 21% there's literally nothing Joe Biden needs to do in order to meet the terms of the deal he made with the other G7 leaders.
If they want to turn this into an international treaty, absolutely, GOP Senate votes will be needed (though, given that the treaty would create a floor that's 6 percentage points below our current tax rate, I would imagine those would be attainable votes—if the GOP created a global floor that was lower than our tax rate, they could use it to argue for lowering our corporate tax rate).