When Trump deals with Democrats, his polls rise. When he picks dumb fights, they fall.

In early September, something odd happened. President Donald Trump's approval rating actually started ... getting better.

Polling averages showed Trump's approval rating rising by about 3 points in the opening weeks of September — up to a peak of 41.7 percent in the RealClearPolitics average and 39.6 percent in the FiveThirtyEight average.

To be clear: Trump's approval rating is still quite bad, particularly for a president in his first year in office. Plus, an improvement of 3 points is a relatively small amount. But after a year when Trump's approval has consistently either stagnated or declined further, it was worthy of note.

More from Vox:
Bill Browder is one of Putin's biggest critics. The US just revoked his visa.
How drug companies make you buy more medicine than you need
Trump's latest big interview is both funny and terrifying

But Trump couldn't keep it going. In the closing days of September, his rating started to fall again, and throughout October it had been either stagnant or slightly declining.

So what changed? It's of course difficult to disentangle what causes overall polling trends in a crowded news environment. And again, this is a relatively small change.

But one potential explanation is that the opening weeks of September more often showcased a President Trump who was reasonably effective, open to compromise, and not embroiled in petty feuds — while October has shown the exact opposite.

It seems like a lifetime ago, but back in the bygone days of early September, the buzz in Washington was all about President Trump's newfound willingness to deal with Democrats.

Trump started off the month by going around his own party's congressional leaders to agree to a government funding deal put forward by Chuck Schumer and Nancy Pelosi. And days later, he met the pair of Democratic leaders again, to discuss a potential deal to protect DREAMers from deportation.

The dealings with Schumer and Pelosi gave Trump something that had been elusive for him: a quick legislative win. Due to the agreement the trio reached, a deal to fund the government and raise the debt ceiling for three months, combined with hurricane aid, passed Congress. Trump, all of a sudden, looked effective.

Meanwhile, the top national news story at the time was the aftermath of the hurricanes affecting Texas and Florida. That was, it seems, a good story for Trump — the federal response was generally viewed as having gone well, and Trump's deal with Democrats got aid money signed into law quickly. Furthermore, disaster response that's viewed as effective can boost a politician's approval rating, as Chris Christie found out in New Jersey.

Now, it would be an oversimplification to say this period was all about Trump doing things Democrats liked. Another major news story at the beginning of the month was the president's decision to end the DACA program, which protects DREAMers from deportation — a decision clearly made to please his base.

But even there, Trump seemed to move quickly back toward the center, at least rhetorically. He called on Congress to pass a legislative solution for the DREAMers, tweeted positive-sounding things about them, and even held that Schumer/Pelosi meeting to try to reach a deal on the matter.

@realDonaldTrump: Congress now has 6 months to legalize DACA (something the Obama Administration was unable to do). If they can't, I will revisit this issue!

@realDonaldTrump: Does anybody really want to throw out good, educated and accomplished young people who have jobs, some serving in the military? Really!.....

It's unclear which, if any, of these matters was most responsible for the small bump in Trump's approval ratings that we saw in the first few weeks of September. Overall, though, the trend seemed encouraging for him, and for his presidency.

But he didn't keep it going. From late September through October so far, Trump's presidency has once again been dominated by stories of petty feuds, partisanship, incompetence, and just general chaos. These include:

1) The feud with NFL players who kneel during the national anthem: At a September 22 rally in Huntsville, Alabama, Trump was speaking extemporaneously and mused that NFL owners should fire players who kneel during the national anthem. This swiftly developed into an enormous national controversy pitting Trump against leading sports figures.

2) Another failed, partisan attempt at Obamacare repeal: After the bipartisan kumbayas of early September, the final weeks of the month in Congress were dominated by a surprising Republican push for the unpopular, partisan Graham-Cassidy bill — an effort that ended in failure.

3) A disastrous response to the hurricane in Puerto Rico: In contrast to the government's generally praised handling of the aftermaths of hurricanes affecting Texas and Florida, the response to Hurricane Maria in Puerto Rico has been heavily criticized and put Trump on the defensive.

@realDonaldTrump: Nobody could have done what I've done for #PuertoRico with so little appreciation. So much work!

4) Morongate: A few news cycles in October were dominated by discussion of reports that Trump's own secretary of state, Rex Tillerson, had referred to the president as a "moron" back in the summer.

5) A feud with a soldier's widow that's lasted more than a week: Finally, and most recently, Trump has spent more than a week arguing with a Democratic member of Congress and the widow of a soldier over whether he was insensitive to that widow during a consolation phone call. Amazingly, this is still going on:

@realDonaldTrump: I had a very respectful conversation with the widow of Sgt. La David Johnson, and spoke his name from beginning, without hesitation!

Now, it would be a mistake to assume that all the bad stories that have dogged Trump for the past month or so have been part of a deliberate strategy on his part. Often, these feuds and controversies have been unplanned or driven by what's at the top of the news (hurricanes, the months-old "moron" comment).

Yet on matters related more to policy, Trump does seem to have deliberately chosen to abandon a strategy that briefly appeared to be improving his popularity and helping him get things done. After dabbling in bipartisan dealmaking for a hot second, he's shifted back to his old preferred strategy of stoking culture-war battles.

Why? Vanity Fair's Gabriel Sherman suggests that one major reason is the defeat of his endorsed candidate Luther Strange in Alabama's Republican Senate primary runoff in late September. "Alabama was a huge blow to his psyche," a person close to Trump told Sherman. "He saw the cult of personality was broken." So perhaps the Alabama result made Trump fear that he's losing his base — and his brand — and made him more eager to stoke feuds and spurn deals with Democrats.

Remarkably enough, though, the combination of all those fiascos in the past month hasn't changed Trump's approval all that much. The upward trend of early September stopped, and Trump's rating has declined by a couple of points since, but 38 percent or so of voters still remain supportive of him. Still, put together all this does seem to have signaled that, no, the president hasn't turned over a new leaf after all.