Is Dennis Prager right about Pope Francis?...

I would say yes with reservations.

In his article posted on Right Wing News , Pope Francis, the Climate and Leftism
(and what's up with those giant pictures of the authors on RWN?  I find them very disconcerting and rather odd.)

To sum up the article, Mr. Prager makes his case for Pope Francis being a leftie with focus on the Pope's upcoming encyclical on climate change which he will present to the UN in September. 

In that assertion, I would have to agree with him.  I think the Pope is a product of his environment and, well, not very smart.  It really pains me to have to say that.

From the article (emphasis mine.)

"How are we to explain that at the very moment that the oldest Christian communities in the world are being violently destroyed; that while Christians are murdered, raped and tortured in Africa and the Middle East; and while horrific barbarities are committed daily in the name of God, the pope issues an encyclical and travels around the world to talk about climate change?"

"It is happening because leftism has taken over much of Catholicism, most of mainstream Protestantism, increasing numbers of evangelicals and most of non-Orthodox Judaism. Not to mention the secular worlds of the news media, entertainment media and academia."

However, Mr. Prager runs off the rails when he states:

In the long run, this will bring down the Church — just as it has mainstream Protestantism and non-Orthodox Judaism — as well as diminish decency on earth.

No, Mr. Prager.  The Church will still be here.  It may be a smaller, and hopefully, a more authentic Church, but God was very clear in scripture when he said, "And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it." Matthew 16:18 

We've had far worse Popes than Francis.  My all time favorite is Pope Alexander VI, of the famous Borgia (Borja) family, who was Pope from11 August 1492 until his death on 18 August 1503.  His entire life was the stuff of soap operas. 

As to the encyclical?  I'll reserve judgement until I read it.  I think it will be a fluff piece saying almost nothing of value.  The danger is the uncatechized Catholics, which nowadays is just about all of them,  the anti-Catholics, and the global warming cheerleaders will latch unto whatever he says and consider it science.  But, then, who are we to judge?