He’s made a million mistakes, I know, and I have opposed nearly all his domestic and international policies. But after watching President Obama’s intense ISIS speech Wednesday night, and reading the text several times, I think the president basically — finally — got it right. I support him. My best advice to Republicans and Democrats is to support the president’s new ISIS campaign.

Noteworthy, as of this writing, is the fact that Speaker John Boehner has announced his backing of Mr. Obama on this matter. Democratic Senate majority leader Harry Reid and Republican Senate leader Mitch McConnell have also announced their support of the president’s ISIS plan. Only Nancy Pelosi is absent.

What I want to underscore is the need for Republicans to get on board with this Obama plan. If not, they risk blowing what appears to be a landslide election. Opposing the president on this would look way too political, ignoring national security. It would be a huge mistake.

Here are the opening words from the president on Wednesday night. They rally support: “My fellow Americans, tonight I want to speak to you about what the United States will do with our friends and allies to degrade and ultimately destroy the terrorist group known as ISIL.”

Importantly, Mr. Obama now seems to be following the sound advice of experts such as former ambassador Ryan Crocker (who terms ISIS, “al-Qaeda Version 6.0”), General Keane, the retired four-star general and former vice chief of staff of the Army, and General Martin Dempsey, chairman of the Joint Chiefs.

Perhaps the most important point in the president’s speech was his apparent decision to bomb ISIS in Syria as well as Iraq. The presumption is that this will be done simultaneously, which is the exact advice given to him by Generals Crocker, Keane, and Dempsey.

That’s another signal to members of the GOP. Before you go home for the congressional election break, fund Mr. Obama’s new military request and pass a resolution endorsing the simultaneous bombing of ISIS in Syria and Iraq.

Additionally, while Mr. Obama said he doesn’t want GI combat troops on the ground, he specifically endorsed the use of special-ops forces to guide enhanced bombing missions and support Iraqi and Kurdish troops with training, intelligence, and equipment.

In his speech, the president announced the deployment of an additional 475 “service members,” which can be added to the several hundred already in Iraq. In all likelihood, thousands of Special Forces will be necessary to destroy the Islamic State. Along with the bombings, there will have to be a ground war to eventually eliminate ISIS. And that will require all manner of U.S. advisors, such as ground-to-air controllers for every allied battalion. This will be tough stuff.

The president also will increase military assistance to the free Syrian opposition to Assad, which is tricky business. But former ambassador Crocker argues that this can be done with moderate Sunni forces.

Mr. Obama stated that “we will redouble our efforts to cut off [ISIS] funding; improve our intelligence; strengthen our defenses; counter its warped ideology; and stem the flow of foreign fighters into and out of the Middle East.” He reiterated the need to provide more humanitarian assistance.

Coalition building will not be easy, but it’s an important part of the strategy. That’s probably why President Obama said, “ISIL is not Islamic.” What he undoubtedly meant is that these are a bunch of crazy, bloodthirsty, power-hungry people who are hiding behind religious beliefs that are not shared by such Arab states as Saudi Arabia, Jordan, Kuwait, and maybe even Qatar. Nor, hopefully, Turkey.

Significantly, Mr. Obama stated a “core principle” of his presidency: “If you threaten America, you will find no safe haven.” Well, that’s basically what President George W. Bush said when he proclaimed right after 9/11 that “You’re either with us, or against us.”

Mr. Obama never gives Bush any credit. He didn’t when his predecessor handed over a stable Iraq following the surge. He hasn’t mentioned that Mr. Bush recommended 20,000 U.S. forces be left behind in Iraq. But at least Mr. Obama has gotten some religion in this new phase of the War on Terror.

Why his change? Well, yes, he’s getting clobbered in the polls. But I think the political narrative completely changed when America saw the beheadings of American journalists Jim Foley and Steven Sotloff. Suddenly, Americans got up and shouted, “We must not let this go unpunished.” Then came the realization that ISIS will come at us at home in a short period of time.

It took President Obama a while to figure all this out. He was leading from behind, but maybe now he’s moving toward the front. Looking ahead, one can predict that the key issues will be commitment and execution.

As President Reagan used to say, “Trust but verify.”