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What a difference events can make.

U.S. airstrikes against ISIS in Iraq remained largely divisive for most of the summer. But our ABC News/Washington Post poll earlier this week found support rising from 54 to 71 percent in just three weeks. The shift, although in line with President Obama's policies, includes many of his political opponents on other issues.

Specifically, the overall increase of 17 percentage points in support for airstrikes since mid-August includes a 22-point leap among Republicans (from 61 to 83 percent) and a remarkable 32-point jump among "very conservative" Americans, from 49 percent to 81 percent.

What's intervened, of course, is the emergence of online videos recording the ISIS murders of American journalists James Foley and Steven Sotloff. Support for airstrikes had already been on the rise among Democrats, in accord with Obama's actions. But it grew especially sharply among Republicans and strong conservatives after the videos became public.

The results make sense: Democrats and liberals were more apt to support Obama's policy from the start. Republicans and conservatives likely needed an impetus from another source.

Regardless of when the trend lines moved, Republicans and strong conservatives are more supportive than other Americans of airstrikes against ISIS in Iraq - a customary result when it comes to military action.

In the meantime, support for the airstrikes is lower among nonwhites - a core support group for the president - and adults younger than 40.

Despite an 11-point bump to 57 percent support in the last three weeks, nonwhites remain one of the groups least supportive of airstrikes against ISIS in Iraq. Among whites, by contrast, support reaches 77 percent. Similarly, just 56 percent of under-40s back airstrikes - including only 44 percent of those age 18-29, another Obama base group. That compares with eight in 10 of those older than 40.