For years, pushing against the ostensibly friendly administration of Barack Obama, environmental activists fought to block the Keystone XL pipeline that would shunt tar-sands oil from Alberta to Cushing, Okla. The argument they presented was not one of geography; it was a demand that the country stop creating infrastructure to continue to facilitate the use of fossil fuels — particularly of the greenhouse-gas-intensive sort that Keystone would transport. Eventually, in 2015, Obama rejected the pipeline by blocking a permit it would need to cross the U.S.-Canada border.

With a flourish of his pen Tuesday, President Trump revived the Keystone project — and the also politically fraught Dakota Access pipeline that was the subject of intense debate that overlapped with the 2016 election.

It’s not clear what Trump’s approval of the projects will mean in practical terms. But the quick reversal highlights a key aspect of American politics today: There are few issues on which there’s a broader partisan split than the issue of climate change.

New data from Pew Research makes that clear.

There’s a fairly wide partisan gulf on the question of “protecting the environment,” as there has been for the past decade. Democrats see this as a bigger priority than do Republicans.

On the specific issue of climate change, though, that split is wider — and widening. (Pew asked about “global warming” until 2015, when it switched to “climate change.” For those curious, the change in terminology is not a function of the world not warming, as some of those skeptical about climate change like to claim; the term “climate change” was first proposed by Republican consultant Frank Luntz.)

The past three years have been the warmest in recorded history, according to government data, during which time the issue has become a bigger priority for the left. Over that same period, it’s stayed flat for Republicans.

In fact, there is no policy issue in Pew’s research where there’s a wider priority gulf between the two parties. Democrats are 47 points more likely to say climate change should be a top priority, a wider margin than the 42-point split on the importance of strengthening the military. In third place is the split over the importance of protecting the environment.

One reason for that split is its overlap with age, as Pew notes. Younger people are more likely to align with the Democratic position on all three of the most divergent policy issues.

These numbers certainly help explain the alacrity with which Trump signed off on the pipeline proposals. (Whether he mentioned the pending approvals in Monday’s well-received meeting with building trades unions — groups that strongly backed the construction projects — isn’t clear.) Republicans, like Trump, are less swayed by the need to take steps that would slow the rate of warming. In January 2015, 80 percent of Republicans approved of building the Keystone pipeline. Democrats disagreed then (39 percent backed it) and disagree with inaction on climate change now — but they just got shut out of power in the nation’s capital.

The key to policy priorities, of course, is having the political strength to enact them.