OPINION — Judging from two House debates this week in hotly contested races on both sides of the country, you would think that the president of the United States was a shadowy, off-stage figure whose personality and politics are barely worth discussing. Even “The Invisible Man” of the 1897 H.G. Wells novel and the 1933 Claude Rains movie had more of a corporal presence than Donald Trump.

During the one-hour debate in Utah’s 4th district in suburban Salt Lake City, the word Trump was not mentioned until the 45-minute mark when the moderator blurted out the president’s name in a question on tariffs.

Describing herself as “a free trader,” two-term GOP incumbent Mia Love avoided using the T-word (Trump, not tariffs) while vaguely boasting that she “has called him out” on trade. Even when she referred to Trump economic advisers Larry Kudlow and Peter Navarro by name, Love never specified where they actually worked.

Her Democratic challenger, Salt Lake County Mayor Ben McAdams, was almost as skittish about naming that man in the White House. In a profile in courage, he once referred to He Who Should Not Be Named in his overall attack on the tariffs by saying, “I will agree with President Trump on one thing: In our trade agreements … we need to be respected.”

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Given the president’s comparative unpopularity in Utah — Trump carried the 4th District with only 39 percent of the vote in 2016 because of the presence on the ballot of third-party independent Republican Evan McMullin — the reluctance by Love and McAdams to invoke his name may have been a geographical quirk.

In contrast, Virginia’s 7th District, anchored in the Richmond suburbs, seems like safe Trump country since the president won the seat with 51 percent even as he was losing the state to Hillary Clinton. But once again, the lone debate between Republican incumbent Dave Brat and Democrat Abigail Spanberger revolved around both candidates taking a vow of silence regarding the president.

[At Debate, Spanberger Reminds Brat He’s Not Running Against Pelosi]

In fact, it seemed like a time warp from 2014. That was the year when Brat, a firebrand conservative economics professor, upset House Majority Leader Eric Cantor in the Republican primary en route to two terms in Congress.

Brat’s three-minute opening statement hit virtually every hot-button right-wing talking point as he railed against “Nancy Pelosi’s liberal agenda,” “open borders,” “sanctuary cities,” and, of course, “Obamacare.” Somehow he missed an attack on George Soros and Bill Clinton’s sexual history.

Spanberger, a former CIA analyst who raised a hefty $3.6 million in the third quarter, played up her biography in the face-off with Brat: “I learned the value of hard work from my mother.” Her attacks on Trump were all by implication as she spoke about how “some people want you to be angry and afraid.”

By The Washington Post’s count, Brat brandished the name Pelosi 25 times during the debate, but the word Trump was only mentioned once. Small wonder that Spanberger said in her concluding statement, “I am not Nancy Pelosi. I am not President Barack Obama.”

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These two Trump-less debates fit a larger national pattern. With the major exception of red-state Republican Senate candidates like Tennessee’s Marsha Blackburn and Missouri’s Josh Hawley, Trump is not a major presence in TV ads. Nor is the president a dominant campaign topic even in Democrat-held open House seats like Minnesota’s 1st District where Republicans are eyeing a pickup.

There are no glib parallels to this odd Trump void. Democrats in 2006 certainly had no hesitation railing against George W. Bush and the Iraq War. Similarly, Obama and his health care program were reviled by Republicans in the run-up to their 2010 landslide.

So how do you explain the Case of the Missing President?

Part of it simply may be that in a political world where everyone is gasping as Trump sucks up all the oxygen, congressional candidates in both parties may want a safe space to catch their breath. In TV ads and debate performances — unlike the rest of life — they can pretend that Congress still matters as an independent branch in the Age of Trump.

But, in truth, Trump is the one who has best expressed the stakes in the 2018 elections. Excoriating the Democrats at an early October rally in Mississippi, he declared, “I’m not on the ticket, but I am on the ticket because this is also a referendum about me and the disgusting gridlock that they’ll put this country through.”

Of course, this election is a referendum on Trump. In fact, it is the only issue that truly matters, no matter how often congressional candidates talk about the deficit or trade or even, as important as it is, health care.

Notice how unchained Trump has become since he began believing that he alone dragged Brett Kavanaugh to confirmation. Most of the lingering constraints on Trump — from curbing his tweeting to minimizing his insults — have vanished in the days since the Kavanaugh vote. In his “60 Minutes” interview, Trump seemed to believe that Charlemagne, Napoleon, Lincoln and Churchill were minor historical figures compared to his own globe-girdling greatness.

Imagine — if you dare — a Trump who feels personally vindicated by a Republican comeback on Nov. 6. There will be no limits to the number of murderous dictators he will embrace, the women he will humiliate and the constitutional norms that he will trample.

For if you believe that the 2018 elections represent just a standard choice of governing philosophies in Congress, then you probably are also still patiently waiting for the 72-year-old Trump to magically mature in office.

Walter Shapiro has covered the last 10 presidential campaigns. He is also a fellow at the Brennan Center for Justice at NYU and a lecturer in political science at Yale. Follow him on Twitter @MrWalterShapiro.