Two months ahead of his first trip to the U.S., Pope Francis' approval rating among Americans has plummeted, driven mostly by a decline among political conservatives and Roman Catholics, according to a new Gallup poll released Wednesday.

Fifty-nine percent of Americans said this month they had a favorable view of the pope, compared to 76 percent in February 2014, Gallup reported. The share of Americans who disapproved of the pope increased from 9 percent to 16 percent in the same period. The changes were most dramatic among political conservatives, whose opinion of Francis nosedived by 27 percentage points to 45 percent. Among Catholics, Francis' approval dropped by 18 percentage points to 71 percent.

The survey was conducted from July 8 to 12, three weeks after the pope released his bombshell teaching document proclaiming climate change largely man-made and excoriating an economic system he said drives global warming and exploits the poor. The survey of more than 1,000 adults had a margin of error of plus or minus 4 percentage points.

When the poll was under way, Francis, the first Latin American pope, was on a homecoming tour through South America that especially unsettled conservatives.

In his July 9 speech in Bolivia — an address that the Rev. Jim Martin, editor at large of the Jesuit magazine America, called Francis' most revolutionary so far — the pope called for radical reform of the global economy and solidarity with the poor, while naming labor, lodging and land as "sacred rights."

Mark Gray, polling director for the Center for Applied Research in the Apostolate at Georgetown University, said the poll reflects that "many American Catholics are more closely affiliated with their political party than their faith." Several Catholics competing for the Republican presidential nomination have criticized or distanced themselves from the pope over his role in the historic thaw in U.S.-Cuba relations and his insistence that unfettered capitalism has hurt the poorest and most vulnerable.

Catholic conservatives have also expressed discomfort with Francis' style and emphasis. Carl Olson, editor of the conservative Catholic World Report, last week wrote that while he agreed with the pope's criticisms of consumerism and overreliance on technology as a cure for society's ills, Olson also found a "weariness" among some Catholics over the tone of many of Francis' sermons and statements, which Olson described as often "haranguing, harping, exhorting, lecturing" and "grating."

However, political liberals also appeared to have soured on Francis, with a 14 percentage point dip to 68 percent since last year. John Gehring, Catholic program director at Faith in Public Life, a liberal advocacy group in Washington, said, "some progressives naively expected him to overturn church teaching on abortion, contraception and same-sex marriage."

Francis raised the hopes of gays and lesbians when he famously uttered, "Who am I to judge?" about gay priests, and said "we shouldn't marginalize these people." Francis has repeated his emphasis on being more open to gays and others, while also reaffirming church teaching on marriage and abortion, most recently in his ecology document, or encyclical, last month.

Gallup also found an increase in people who said they had no opinion about the pope or hadn't heard of him, rising from 16 percent last year to 25 percent this month.

After his surge in overall popularity last year, the pope's approval ratings are now back to the level they were soon after he was elected in 2013, according to Gallup. The Pew Research Center found a similar if less dramatic pattern, with a peak in Francis' favorability at 70 percent this past February and a drop to 64 percent last month.

Francis is due to arrive in Washington, D.C., on Sept. 22, and will also travel to New York and Philadelphia. One of the most-watched events will be his Sept. 24 speech to a joint meeting of Congress, where Republicans have largely ignored his climate change encyclical. Francis added a Cuba leg onto the beginning of the trip, from Sept. 19-22.

Christopher Bellitto, a church historian at Kean University in New Jersey, said the decline from such a high-level of popularity was not surprising. "Who can sustain those numbers for that long?" Bellitto said.

"Whether liberal or conservative, you love the pope when he agrees with you," Bellitto said. "And he's been saying things that annoy both sides."