For weeks, even months, Democrats have been salivating — and Republicans getting dyspeptic — over the prospect of a “wave” mid-term election that will sweep them into power in both the House and Senate. But there’s ample reason to believe that this wave will never materialize and that Republicans may be safer on the beach than most believe.

President Donald Trump’s approval ratings hover around 40 percent, and conventional wisdom has it that his unpopularity will rub off on other Republicans. This is certainly true — but its effect is limited by the fact that Trump is a singular figure.

Even Washington Republicans — some in his own administration — have been overheard by reporters muttering that the president is out of his mind, or words to that effect. Members of Congress didn’t elect Trump, though they can be blamed for supporting most of his policies. Many of those policies, however, could well be perceived by voters as bearing fruit — even if some see Trump as a little nutty.

Those anticipating a Democratic wave must understand, first, that most of the public now considers the economy to be in great shape. That is a critical issue when it comes to getting elected. Remember the presidential campaign of the Democrats’ own Bill Clinton coined the phrase, “The economy, stupid.”

A January Quinnipiac poll found that 66 percent of U.S. voters believe the economy is "excellent" or "good," up from 63 percent in December. This is the highest positive rating of the economy since the poll first asked the question in 2001.

Those anticipating a Democratic wave must understand, first, that most of the public now considers the economy to be in great shape.

Trump, however, is not given particular credit. Only 37 percent of respondents say his policies are helping the economy. In fact, 49 percent say former President Barack Obama is more responsible for the strength of the economy, while 40 percent say Trump is more responsible than Obama. Either way, the economy is good, and people are feeling it.

And the economy looks unlikely to change for the worse anytime soon. Many forecasters predict growth at close to 3 percent for the rest of the year. Jobs are abundant and unemployment is shrinking. In mid-January, jobless claims were at a 45-year low.

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What’s more, the benefits of the tax cut passed in December are going to be pressing directly on the pleasure-sensation zone of workers’ brains all year. The new money is due to start showing up in paychecks by mid-February.

If voters start to forget about or overlook this benefit, Trump is certain to keep blasting all the good economic news on his Twitter feed right up through Election Day. He won’t make the same mistake as Obama, who failed to successfully publicize middle-class tax cuts that were included in the 2009 stimulus bill. Most people didn’t even know they had gotten a tax cut.

Another problem is that Democrats do not appear to have much of an agenda beyond helping illegal immigrants — over which they nearly shut down the government before backing off. Democratic leadership backed off for good reason: Relatively speaking, no one cares.

Only 5 percent of Americans listed “Immigration/illegal immigrants” as their top concern in a December 2017 Gallup poll. The other big Democratic focus, the Russian investigation, is even less of a priority. Fewer than 0.5 percent cited the “Situation with Russia” as their biggest issue, despite constant efforts by Democrats and the press to highlight it.

A December 2017 AP poll showed that health care and the economy matter far more to Americans, all things considered. Only 38 percent said “the Russia investigation” was very or extremely important. Compare that to the 85 percent who said the same about health care, 83 percent who gave that rating to the economy and 78 percent who felt that way about taxes.

Special counsel Robert Mueller’s probe could even provide Trump grounds for a series of triumphant I-told-you-so tweets — should Mueller exonerate him. On the other hand, a finding of wrongdoing, though possibly harmful to Republicans, could stir the GOP base to turn out for the midterm election and vote to protect Trump against impeachment by a Democratic House. This could mitigate the expected large turnout of the Democratic base, which is already highly motivated.

One potential bright spot for Democrats is that Gallup found Americans’ top concern to be “dissatisfaction with government/poor leadership.” The bad news? Dissatisfaction with government is nothing new — running at about the same level it has for a decade, with around two-thirds of Americans saying they don’t like the way the nation’s affairs are being handled. Creating divided government, by giving the Democrats control of the House or the Senate, is hardly the ideal way to make government more effective.

Besides, Democrats are unlikely to rally on Election Day to put House Minority Leader Nancy Pelosi (California) and Senate Minority Leader Chuck Schumer (New York) in charge of Congress. Neither polls above 50 percent — among Democrats.

It is true, though, that Democrats are ahead on the average of “generic” ballots — poll respondents say by an average of about 7 points that they would back a Democrat over a Republican in Congressional races. But the gap declined steeply during January, from a high of about 13 points.

One potential bright spot for Democrats is that Gallup found Americans’ top concern to be “dissatisfaction with government/poor leadership.”

In any case, early generic ballots are not reliable indicators of a wave — as the last three non-presidential year wave elections show. In the 2010 election, the midterm when Obama said the Democrats got a “shellacking,” the generic ballot had Republicans only barely ahead until late July, when the gap began to broaden. That November, Republicans picked up 63 House seats and six Senate seats.

In 1994, some generic ballots put Democrats ahead — including ABC News, which had Democrats leading right up until Election Day. Then Republicans stole Congress from the Democrats for the first time in 40 years. The GOP won 54 seats in the House and eight in the Senate. On the other hand, the 2006 generic ballot consistently showed Democrats well ahead, and they took over the House and Senate, winning 31 seats in the former and six in the latter.

There is one other issue that could send the president’s approval rating soaring. It’s rarely mentioned in terms of its political effect, though. Perhaps because people are hoping, as they have for more than two decades, that the problem will somehow go away. This is the year something must be done, or not, to stop North Korea from developing a nuclear weapons arsenal that can attack the United States.

The signs are that Trump is inclined to face this existential menace. Eradicating the threat might take removing Korean strongman Kim Jong-Un from power, whether through economic or military pressure. Such a confrontation — even if difficult and costly — would likely result in a rallying around the flag and the president that would not dissipate before Election Day.

If this happens, Republicans who today don’t want Trump within a thousand miles of their campaign rallies might suddenly beg for an appearance. And Democrats will find their hopes of taking Congress are history, just like as Kim.

Keith Koffler is the editor of White House Dossier and the author of “Bannon: Always the Rebel."