The midterm elections are shaping up to be a debacle for House Republicans. They may take solace in the challenge of replacing 44 Republican seats vacated by retirements and the fact that, since World War II, incumbent presidents’ parties have lost an average of 26 House seats in the midterm elections.

However, this year’s devastation owes much to their inability to deliver on many key Republican priorities and disciplined Democratic messaging.

By any reasonable measure — growth, unemployment and the progress of minorities — President Donald Trump has delivered but former President Barack Obama has kept the economy in play by arguing his administration laid the foundation for Trump’s success.

Corporate tax cuts and deregulation do matter but Obama is simply more credible with swing voters. Democrats repeat his claims consistently and for many voters in swing districts, those become the truth.

They use the minimum wage issue to harp on inequality — code for what good is more rapid growth if workers at the bottom are on food stamps — but the fact is lower-paid workers are now getting outsized wage increases. And Democrats have been effective with the narrative that the recent personal tax cuts favor the wealthy when it’s the nurse not the doctor that often gets the benefits.

With the repeal of state and local tax deductions, high-income suburbanites in places like New York, New Jersey and California face tax hikes and will likely abandon the Republican Party. Its candidates can blame Trump and Treasury Secretary Steven Mnuchin for caving to the Koch brothers and Walmart WMT, +0.90% by not applying the corporate tax to imports and rebating it on exports. That would have generated $1 trillion in additional revenue and permitted tax reductions for everyone — and helped reduce the trade deficit too.

Other than the steel and aluminum tariffs, the president’s trade policies have largely not delivered for manufacturing workers, and farmers hit by foreign retaliation are worse off.

The deals struck with Mexico and South Korea are largely defensive. Those will limit further losses to China in the auto parts, technology and several other industries but won’t move the needle on the trade deficit.

Regarding China, Trump really needs for our allies to impose tariffs or other limits on their imports from the Middle Kingdom to force Beijing into meaningful systemic reforms. However, by taking aim at all our allies with the metal tariffs, when the Commerce Department offered him the option of aiming those solely on big malefactors like China and Turkey, he nixed the possibility of strong, coordinated Western actions to combat Beijing’s cheating on trade.

On immigration, the president may be making some progress but his obsession with a border wall makes little sense. And, the fiasco surrounding the separation of children from parents just doesn’t sit well with most decent people.

Neither the president nor Republicans on Capitol Hill have been able to convince voters about their support for common-sense immigration reforms based on the Canadian model of emphasizing labor force need, skills in short supply and genuine refugees. Many Democrats may favor similar reforms but the issue has been seized by hard-left Democrats to paint the president as racist and that virtually all immigration is good for the economy.

We were promised a big infrastructure program. Getting Democratic cooperation on spending for roads should have been easy but Transportation Secretary Elaine Chao has not come up with a package.

Republicans simply won’t accept that folks who use the roads should pay for them with higher gas taxes. Or that Americans pay way too much to lay tar and tunnel thanks to pork-barrel spending appropriated by both parties and inflated costs imposed by unions through the Davis-Bacon Act.

On health care, the Republicans failed to deliver a better plan than the Affordable Care Act. Americans may have been glad to be rid of the individual mandate but they remain upset about rising premiums, drug companies’ profiteering, and hospitals monopolizing local markets. They remain fearful of losing coverage for pre-existing conditions. The Democrats have managed to turn those issues so that voter approval of the ACA is near an all-time high.

As with other issues, unless Republicans learn to rail against monopoly exploitation with the zeal and discipline of Democrats, they lose.