I have supported the notion of a check and balance for pardons. Something along the lines of a constitutional amendment that allows for the negation of a pardon if two thirds of the senate dissent. If the person pardoned is not ‘arm’s length’ from the president, or if it smells of corruption or payoff, the Senate (or the House, or either can negate it). Maybe it would not happen often, but the possibility of negation might prevent a ‘deal’ that buys the silence of a convicted crony of a president.
If you are going to go this route two thirds is too high.
That is an impossibly high hurdle. It is almost impossible in most cases that you will ever get a two thirds majority to override a pardon.
I doubt that a pardon would ever even be brought to the floor for debate.
Just consider how often a veto is overridden.
How often are judges impeached.
These are things much more consequential.
It is very unlikely that a Senator is going to expend political capital to go against a pardon of a President of his own party to block a pardon.
It’s not worth it.
I think three fifths would be a difficult hurdle to overcome.