WASHINGTON — Jeb Bush and Hillary Clinton have a shared interest: Each wants to act as if the primaries are over and that the general-election campaign — between, each hopes, the two of them — is already underway.

Bush, who has been flat in the polls, has a particular need: to shift a Trump-saturated discussion of who is the most flamboyant personality toward a conversation about which Republicans might plausibly be president of the United States.

To that end, Bush offered a political science lesson in his major foreign policy speech on Tuesday: Republican voters have radically different views on the topic from those of Democrats and also give security issues a much higher priority. This is why Jeb Bush decided that broadly allying himself with his brother’s international approach will help him more than it will hurt him — at least during the primaries.

In a normal (meaning Trump-less) campaign, Bush’s address at the Ronald Reagan Presidential Library in California would have made more of a splash. The same is true of Clinton’s earlier speech outlining an ambitious proposal to deal with the debt loads faced by college students.

Not very long ago, candidates actually competed, at least some of the time, on ideas. Big think speeches of the sort Bush and Clinton gave (along with college-debt proposals by Clinton’s Democratic rivals, the ascendant Bernie Sanders and Martin O’Malley) would be at the center of the coverage. But Trump is so much more fun, and he’s not wrong to think he’s driving television ratings.

So let’s pretend Trump didn’t exist and notice the different places where Bush and Clinton want to take the campaign, Bush to foreign policy and Clinton to domestic concerns related to economic fairness.

The explanation? As my Brookings Institution colleague William Galston has pointed out, Republicans and Democrats disagree not only on issues but also on which of them really matter. He cited a Bloomberg/Des Moines Register poll released in June. Here, in order of importance, are the problems Iowa Republicans listed when asked what they wanted their candidates “to spend a lot of time talking about”: the budget deficit, national defense, taxes, terrorism, job creation, immigration and trade. And here are Iowa Democrats’ top issues: energy, income inequality, infrastructure, job creation, immigration and college costs (tied for fifth), and climate change.

Note that two issues related to national security are on the GOP list and none is on the Democrats’ list. Only job creation and immigration made both.

So Bush’s attack on Clinton and President Obama for what he called their “blind haste” to get out of Iraq certainly played well with the GOP voters — even as Democrats were absolutely certain that Bush was making a grave error that will haunt him in a general election. “This speech is clear proof that his brother’s unrepentant neocon crowd are in full command of @JebBush foreign policy,” Sen. Chris Murphy (D-CT) tweeted during Bush’s address, adding: “Ugh.”

Jeb’s defense of the surge of American troops in Iraq that George W. Bush initiated as a “brilliant, heroic and costly” success likely helped with Republicans, too. The Bloomberg/Register poll found that 57 percent of Iowa Republicans thought it would be “mostly good” if Jeb had W. as an advisor, while only 33 percent thought it would be “mostly bad.”

Making the best of his brotherly loyalty is Jeb’s imperative, even as he struggles to find ways of putting distance between himself and the original choice to go to war in Iraq. “No leader or policymaker involved will claim to have gotten everything right in the region, Iraq especially,” he said. Ah, the power of understatement.

Yet in this year’s odd dynamic, Bush’s aggressiveness is also giving Clinton a hand, by linking her with Obama (yes, he’s very popular among Democrats) and with the decision to bring an end to the Iraq War (also popular in the party). His speech also allowed her to go on offense at a moment when media stories were focusing on her decision to turn over her world-famous email server to the FBI.

John Podesta, Clinton’s campaign chairman, no doubt enjoyed taking to Twitter on Wednesday morning to pounce on Bush: “Chutzpah: Jeb blaming Obama for W’s failure in Iraq. Must have forgotten it was Bush-Cheney who blew it there. Now he wants a do over? Plz..”

Plz indeed. Clinton relishes the fight Bush has initiated. And it’s a scuffle that Bush hopes will draw at least some eyes away from the spectacle that is Trump.

E.J. Dionne’s email address is ejdionne@washpost.com. Twitter: @EJDionne.

Photo: 2016 Republican U.S. presidential candidate and former Florida governor Jeb Bush is the first candidate on stage before the start of the Voters First Presidential Forum in Manchester, New Hampshire, August 3, 2015. REUTERS/Brian Snyder