He’s doing the right thing, though there will be criticisms back home…

Louisiana’s Bobby Jindal has become the first Republican governor to defy Chris Christie by helping cash-strapped Rob Astorino raise funds to challenge Gov. Cuomo, The Post has learned.

Jindal, like New Jersey’s Christie a potential presidential candidate in 2016, agreed last week to host a big-ticket fund-raiser for Westchester County Executive Astorino in Manhattan on Oct. 16, 2¹/₂ weeks before Election Day and in time to help fund a last-minute TV blitz to bolster Astorino’s financially hard-pressed campaign.

“Gov. Jindal believes this race is winnable by Rob, and he wants to come in, and he’ll be doing the fund-raising event for us,’’ Astorino spokeswoman Jessica Proud told The Post.

“He has a very good donor list in New York City, and he’s going to be very helpful,’’ she continued.

Jindal’s decision is a “shot across Christie’s bow, and there’s no love lost there,’’ said a prominent New York Republican.

Christie, who took over for Jindal as head of the Republican Governors’ Association, set up something of a non-aggression pact with Andrew Cuomo after the Bridgegate scandal hit in New Jersey. Cuomo didn’t attack Christie for Bridgegate, and in return Christie hasn’t hit Cuomo over his corrupt actions in the Moreland Commission case. It’s all quite cozy among the two governors, though it’s a complete sellout of the Republican Party and a disservice to the people of New York who aren’t being given a shot at a viable alternative to Cuomo.

Christie says Astorino is a “lost cause.” That is the typical cowardice and sloth of the East Coast GOP establishment at work. A New York governor’s race is a “lost cause,” just like the black community is a “lost cause” and young voters are a “lost cause.” Or if they’re not lost causes then the principles of the party must be abandoned in order to pander to those votes.

Jindal should get credit for riding to the rescue in New York, lost cause or not. There are congressional races in New York this fall, and if helping Astorino make a fight of the governor’s race there has the effect of turning out more Republicans on Election Day perhaps a side effect will be winning one or two of those congressional races. Not to mention that once Cuomo wins re-election he’s going to turn his attention to 2016, and he’s a decent bet to run against Christie and Jindal. Why you wouldn’t want to dirty him up in advance of that is a pretty obvious question.

As for Christie, he’s an embarrassment to the party.

But back in Louisiana, there will be grousing about Jindal’s involvement in New York. People will ask why he’s not more involved in the Senate race, for example, or why he’s not helping Keith Gates knock off Foster Campbell and thus dramatically change the ideological makeup of the Public Service Commission. Or why he isn’t involved in the 5th or 6th District congressional races. Now, you could argue that Jindal is past the point where he has the ability to positively affect any of those elections – but we do know that Jindal can help raise a lot of money for folks he’s friends with, and there are some good candidates in those races who could use that help.

Perhaps he’s past that. Jindal is less than 18 months from the back door of his governorship, and he’s looking toward national political prospects right now. His actions will have to be evaluated on that basis, and maybe we’ll just have to accept that he’s an absentee landlord as governor much like Mike Foster was at the end of his second term.

Foster spent time on his motorcycle and at Southern’s law school. Jindal is speaking in Iowa and raising money for candidates in New York. The latter might be more productive.