Pedro G. Espada, son of state Senate Majority Leader Pedro Espada Jr., re signed yesterday from his new $120,000-a-year Senate job after Attorney General Andrew Cuomo began probing the hire — and a Post investigation exposed him as a clueless no-show.

But that doesn’t mean Cuomo should drop the probe. To the contrary.

The job for Junior was almost certainly part of the spoils Sen. Espada extorted from Senate Democrats last month in exchange for his return to the fold — the same transaction that made him titular head of the entire chamber.

Indeed, The Post’s Fredric U. Dicker and Brendan Scott report today that a senior Senate Democrat says Espada personally demanded the post for his son.

Which raises the question: If Espada and the Senate Dems were willing to be that shameless, what else will Cuomo find — if he looks?

Espada and co-conspirator Sen. Hiram Monserrate had both parties bidding against each other for a month as the chamber descended into chaos.

What nefarious deals were offered?

Which ones were accepted?

Transactional politics, to be sure, have always been part of the game.

But there are limits — imposed both by the dignity of office and the law.

The Senate, alas, gave dignity a firm drop-kick long ago.

But enforcing the law is Cuomo’s duty.

Espada, certainly, is a ripe target:

* He was indicted in ’98 for stealing more than $200,000 in Medicaid cash meant for his Soundview Health Center in order to finance his and his son’s political campaigns. Though he was acquitted, three Soundview employees pleaded guilty to much the same offense.

* A top Soundview official pleaded guilty in 2001 to falsifying documents that diverted nearly $100,000 to the center from another nonprofit.

* Espada went 10 years without filing campaign-disclosure reports — racking up $61,000 in fines and leading to speculation that he’s still using Soundview as his personal and political piggybank.

Cuomo is already looking into that.

Now he needs to examine the Senate.