(CNN) As the confrontation with North Korea deepens, Donald Trump is confronting doubts about his leadership at home and abroad that are almost unprecedented for a US president during a time of international crisis.

These swirling misgivings, exacerbated again this weekend by Trump's widely criticized response to the violence in Charlottesville, Virginia, present the President with unique challenges as he tries to rally the country and the world in the stand-off with North Korea.

Given the underlying questions about his leadership, Trump faces the real risk that his belligerent "fire and fury" language -- even if intended to create pressure for negotiations, as some experts believe -- may be unsettling the public in the US and its key allies more than it rattles mercurial North Korean leader Kim Jong Un.

"It's quite difficult to do this without domestic opinion, especially if you are going to do the kind of brinksmanship he is doing right now, which has huge risks," says James Steinberg, the former deputy secretary of state for Barack Obama and deputy national security adviser for Bill Clinton. "If you don't have the American people behind you and you get into these huge exercises of drawing red lines, where are people going to be if he gets them into a conflict?"

Lower approval than previous Presidents in international standoffs

Even before Trump sparked outrage last weekend by failing to initially condemn white nationalists for the violence in Charlottesville, he was operating with a lower job approval rating than almost any other president during a national security standoff since the Cuban missile crisis between the US and then-USSR more than 50 years ago.

In daily Gallup polling, Trump's approval rating has oscillated between 36% and 40% since late June, though on Monday he skidded to just 34%, his lowest mark ever in the survey. (The most recent CNN poll put Trump's approval at a comparable 38%, also his lowest mark in that survey.)

That's a weaker position than almost any other president has faced at other moments of tension. In Gallup polling, John F. Kennedy's approval rating stood at 63% just before the Cuban missile crisis in 1962. George H.W. Bush enjoyed a 60% approval rating before he launched the first Iraq War in 1990, and his son George W. Bush stood at 58% before he started the second war there in 2003. Bill Clinton stood at 53% when he launched the bombing of Bosnia in 1995 and 62% when he ordered the Kosovo bombing in 1999. Richard Nixon enjoyed a solid 56% rating before he invaded Cambodia in April 1970. Lyndon Johnson (at 48%) just before the 1968 Tet Offensive in Vietnam and Ronald Reagan (at 45%) just before the 1983 Marine barracks bombing in Lebanon were in weaker positions than those other presidents, but still stronger than Trump is today.

Only Jimmy Carter at the outset of the Iran hostage situation in November 1979 began an international stand off in a comparably weak position: in Gallup polling just before the hostages were seized, Carter's approval rating reached just 32%. And Trump's current Gallup disapproval rating (61%) is even higher than Carter's (55%) was then.

Beyond this general discontent about his performance, Trump in polls is also facing specific doubts that could inhibit his ability to build support in Congress and the country for his confrontational approach to North Korea. In the latest CNN national survey , fully 60% of Americans said they did not consider Trump to be honest and trustworthy; the most recent Quinnipiac University national survey found that an overwhelming 71% of Americans (including over one-third of voters who lean Republican) do not consider Trump level-headed. Most directly, both a CBS poll earlier this month , and an ABC/Washington Post survey in July , found that only about one-third of Americans were confident about Trump's ability to handle the crisis.

Increased isolation

More subjectively, the Charlottesville backlash appears to be accelerating a process of isolation for Trump. Compared to earlier in his presidency, more Congressional Republicans felt comfortable -- or even compelled -- to criticize him for his refusal on Saturday to directly renounce the white nationalist and racist groups that descended on the city. Under pressure, Trump did issue strong language when he made a statement Monday. Similarly, over his turbulent first months, more leaders in other segments of society have grown wary of identifying too closely with him, a process symbolized by Monday's resignation from Trump's business advisory council by Merck & Co CEO and board chairman Kenneth Frazier, one of the few African-American CEOs of a Fortune 500 company. From the outset, Trump has also faced unprecedented public questions about his fitness from former top national security and intelligence officials in both parties.

All of these dynamics mean that if Trump turns to military action against North Korea, he would likely have far fewer outside voices validating his choice than a president can usually call upon.

Concern abroad

Internationally, Trump has run into an even more imposing wall of skepticism. Global polling this year from the Pew Research Project found that preponderant majorities of the public in key US allies describe Trump as not qualified, arrogant, and dangerous, with large majorities saying they do not have confidence in his ability to do the right thing in world affairs.

Those feelings are especially intense in several of the countries on the front line of the crisis. In the Pew polling, just 17% of adults in South Korea said they had confidence in Trump to do the right thing in world affairs and just 18% called him well qualified to be president, while 76% said he was dangerous, and 85% called him arrogant. In Japan only 24% said they had confidence in Trump, while a mere 15% called him qualified; that was far less than the 56% who termed him dangerous. Trump's numbers were comparably poor in Australia. In all three countries, Trump inspired far less confidence than not only Obama, but also George W. Bush, who provoked his own international doubts, in the global Pew surveys.

Peter Feaver, a Duke University political scientist who served as a senior adviser on the national security council for strategic planning under Bush, says these international doubts won't make it impossible for foreign leaders to back Trump if they support his strategy -- as demonstrated by the unanimous recent United Nations vote tightening economic sanctions on North Korea. But these widespread reservations, he adds, will make other leaders more cautious about supporting his initiatives. "It means you are carrying a few more rocks in your rucksack as you walk up that hill," Feaver says.

Against these headwinds, Feaver and other experts say, Trump has two major assets in building support for his North Korean brinksmanship. One is that the American public does see North Korea as a genuine danger: In a Chicago Council on Global Affairs survey released earlier this month, three-fourths of Americans described North Korea as a critical threat to the US.

Trump's other asset is that Americans recognize the diplomacy-centered approaches to North Korea employed by Presidents Bill Clinton, George W. Bush and Barack Obama have failed to materially slow the advance of its nuclear weapons program. Americans understand "this is not a problem of Trump's making," Feaver says. "Everyone knew this was coming due."

But Trump, Feaver adds, has created new problems by so relentlessly questioning the competence and loyalty of the intelligence community -- whose assessments inevitably would provide the foundation for any possible preemptive attack on North Korean nuclear facilities. "If what you are talking about is a preemptive or preventive strike on North Korea, that looks a heckuva lot like Iraq in strategic construction," Feaver says. Given that, he continues, Trump's own denunciations of the intelligence community, including for its failures in Iraq, has made it "harder to make a compelling case to the American public than it otherwise would have been."

Steinberg points to a similar problem in mobilizing international opinion for any military strike, particularly in Asian nations. In effect, Steinberg notes, the US viewed a growing North Korean nuclear capacity that could reach South Korea or Japan as a threat, but not a sufficient cause for preemptive war. Now, though, Trump is suggesting he would initiate military action before North Korean missiles can reach the US, even if the consequence is massive retaliation from North Korea against South Korea and Japan. Republican Sen. Lindsey Graham said Trump made that thinking explicit last week when he told him, "'If thousands die, they're going to die over there. They're not going to die here.'"

Steinberg, now an international affairs professor at Syracuse University, says such arguments play "right into the hands" of Kim Jong Un. "His whole strategy is to drive a wedge between the US and South Korea ... and we are playing right into this by convincing them that we not taking the South Korean interests into account," Steinberg said. "That's his argument to the South Korean people: 'You are betting on these guys, and their belligerence is at your expense.'"

All of these considerations point to the same sobering conclusion: It is no longer a theoretical question whether a president standing on a cracked foundation of public confidence can mobilize the world to defuse a crisis whose complexity and consequences may be unmatched since John Kennedy and Nikita Khrushchev went eyeball to eyeball over Cuba.