A scandal out of Boston is pretty embarrassing for all those Democratic Party claims to be concerned about dirty money in politics.

Liberal politicians across the country are rushing to return donations from the small Thornton Law Firm, a personal-injury shop that used “bonuses” to reimburse at least $1.4 million of partners’ political donations.

Holier-than-thou Sen. Elizabeth Warren (D-Mass.) and her PAC hauled in nearly $130,000 in Thornton money.

Worse, she at first refused to give the cash back after The Boston Globe broke the story — bending only after Hillary Clinton, President Obama and others did the (obvious) right thing.

It looks like a classic “straw donor” operation: That’s when the giver of record isn’t really paying the funds, allowing an illegal end-run of donation limits.

The firm insists its setup was kosher, as the partners were still spending their own money, since they own the firm that was reimbursing them. But the scheme still left them down no cash out of pocket — which sure makes the “gifts” look like the firm investing in politicians who’d serve its needs.

Indeed, Thornton got into the political-giving game when then-President George W. Bush started pushing reforms that would let asbestos victims get paid without having to fork over a third of their awards to lawyers.

In fact, the firm’s lawyers apparently gave to only one Republican over the years: Sen. Lindsey Graham, who was key in killing the Bush reform. An even bigger winner was then-Sen. Joe Biden, who actually blocked the “asbestos trust fund” twice.

Also scoring big was New York’s own Sen. Chuck Schumer — who’s set to lead Senate Democrats come January.

As it happens, Schumer just this year helped kill another bid to cut lawyers out of the lucrative asbestos action, by burying the House-passed Furthering Asbestos Claim Transparency Act in committee.