For the first time ever, half of Americans say they believe in climate change and that they are very concerned about it, according to Gallup.

Thanks, President Trump.

Climate change is merely the latest issue on which the American people have moved appreciably and significantly to the left in the Trump era. While it's difficult to ascribe any one of these shifts to Trump specifically, the pattern is becoming clearer. And there's growing evidence that Trump is unifying half (or more) of the country against things he has vocally supported — in ways they simply weren't unified before.

The most recent example is Gallup's climate change numbers. For years before Trump's campaign, fewer than 40 percent of Americans were what Gallup labels “concerned believers” — i.e., they believed climate change was real and a very serious threat.

Office of Management and Budget Director Mick Mulvaney says President Trump’s position is that “we’re not spending money” on climate change research “anymore.” (Reuters)

The number ebbed as low as 33 percent midway through President Barack Obama's tenure — after Obama failed at cap and trade legislation and was pursuing global climate pacts — but it now stands at 50 percent early in Trump's presidency.

Ditto Obamacare, which in the midst of the GOP repeal effort has risen to new highs in popularity.

The Kaiser Family Foundation tracking poll two weeks ago showed that 49 percent now had a favorable opinion of the Affordable Care Act — up from the mid-30s as recently as 2014.

The Pew Research Center also showed Obamacare hitting a new high last month, at 54 percent approval. That was the first time it had majority support.

It's also now apparently happening on the Keystone XL pipeline. The same Pew poll showed what was once an overwhelmingly popular project is suddenly polarizing — with more opposition (48 percent) than support (42 percent).

President Trump unveiled his administration's official go-ahead for the Keystone XL pipeline, a controversial project that was rejected by his predecessor, former President Barack Obama. (Reuters)

As recently as 2014, Americans supported the pipeline nearly 2-to-1.

A more long-running example of this is Trump's U.S.-Mexico border wall. While it had been a somewhat popular proposal for years, Americans have now turned against it pretty strongly. And that's been even more evident as Trump turned it into a rallying cry at his campaign events.

As the Monkey Cage wrote last year, support for the border wall fell during the campaign by about 10 points in three separate polls.

A big reason for the decline, UC-Irvine professor Michael Tesler noted, was that Trump opponents rallied to the view he opposed. Here's how that looked:

And there's evidence that the same thing is happening with these other issues. Most glaringly, that's the case with the Keystone XL pipeline, which used to have strong support from all but the most liberal Democrats.

Just four years ago, 35 percent of Democrats and Democratic-leaning voters opposed Keystone; today, 74 percent oppose it.

That's because the issue moved out of the abstract when Trump signed an executive order beginning its construction. It also meant the project suddenly became tied to Trump's brand.

That Trump brand keeps falling. A new Gallup tracking poll Monday — the first since the health-care bill imploded — showed his approval rating hitting a new low of 36 percent. That's lower than Obama ever got in his entire eight years.

It seems all Democrats needed to do to get people to buy into Obama's environmental, immigration and health-care agendas was to allow a severely unpopular GOP president to succeed him.