Protesters take part in a "No Ban, No Wall" rally in Austin on Feb. 25, 2017. (Eric Gay/AP)

At the end of 2009, the end of the first full decade of the 21st century (at least under the popular definition), Gallup's pollsters offered a review of Americans' attitudes about the preceding 10 years. It included an overview of one of their long-standing metrics, the issues that Americans are most likely to cite as the most important problem facing the country.

The four issues that dominated the decade moved like this.

(Gallup, Dec. 2009)

Seventeen years after the Sept. 11 attacks, a period that often seems to have been defined by that event, it's interesting to note how Gallup described the sudden spike in concern about terrorism — and what happened to that concern shortly afterward.

"Two of these four issues — terrorism and wars — were basically not on Americans' radar in the first year and a half of the decade. That changed after the Sept. 11, 2001, terrorist attacks," Gallup's team writes. "Mentions of terrorism as the nation's most important problem went from zero in early September 2001 to 46% in October of that year. Concerns over terrorism began to decline from that point on, and by decade's end, only 1% to 2% of Americans were mentioning terrorism as the country's top problem."

By 2007, terrorism didn't crack the 10 percent mark in terms of the density of people citing it as the top problem.

Those data, though, go only until the beginning of 2010. We went through Gallup's archives and pulled out the next eight years' worth of data, to get a sense of how that might have changed.

The most obvious trend, already apparent in Gallup's graph above, is the emergence of economic issues as a central concern. At least 40 percent of respondents consistently cited the economy as the most important problem until late 2014. In the years immediately after the recession, there was an accompanying concern (a subset of the economy number): The size of the federal budget deficit. By 2015, that concern had receded.

(Philip Bump/The Washington Post)

For several years after Gallup's review, terrorism continued to meander along at 1 or 2 percent. That changed in late 2014, when the issue started to gain a bit more traction. It spiked in December 2015 after the attack in San Bernardino, Calif., and generally remained at or higher than 5 percent until early 2017.

(Philip Bump/The Washington Post)

Why did that shift happen? In large part because of politics. Ahead of the 2014 midterm elections was a heavy emphasis on the threat posed by the Islamic State, and the rise of the candidacy of Donald Trump put a strong focus on terrorism as a threat facing the country. In the wake of a mass shooting in San Bernardino, Trump proposed a ban on Muslims entering the United States that largely came to define his campaign.

Well, that and immigration. Immigration, too, gained traction in 2014 as the influx of young migrants fleeing violence in Central America rose to national attention — and became a target of rhetoric among conservative media outlets. That focus on immigration as a problem continued through the campaign and the first year of Trump's presidency.

This year, as Trump has hammered on it before the midterm elections, immigration has surged as an issue of concern. In July, more people cited immigration and undocumented immigrants as the most important problem in the country than the economy.

(Philip Bump/The Washington Post)

Thanks to a surge at the beginning of 2017, the category of "dissatisfaction with the government" had been the most consistently cited problem. (This, too, of course, can be credited to Trump, although from the other side of the political spectrum.) Since August 2017, dissatisfaction with government has been more commonly cited than economic issues, but it, too, was passed by immigration in July.

(Philip Bump/The Washington Post)

While we're on the subject of how concerns cited by Americans affected the 2016 campaign, we should note the rise in concerns about race relations in late 2014, overlapping with the emergence of the Black Lives Matter movement. Those concerns have remained fairly steady for some time, spiking in July 2016 after a mass shooting in Dallas resulted in the killing of five police officers.

(Philip Bump/The Washington Post)

Politics and political rhetoric obviously and understandably influence how people answer this question from Gallup. Given Tuesday's anniversary of the 9/11 attacks, it's worth considering how that interplay can work.