Brian Klaas is a fellow in comparative politics at the London School of Economics and author of the book, "The Despot's Apprentice: Donald Trump's Attack on Democracy." The opinions in this article belong to the author.

(CNN) 2017 is the year we somehow got away with it.

Last year, despite having an unprepared, uninformed, reckless conspiracy theorist in the White House, there was no global conflagration.

American democracy was threatened, but not destroyed. 2017 was the year the Trump administration transformed the American presidency into a reckless reality show, created needless volatility and savaged America's international reputation -- but many of the most-feared cataclysms did not come to pass.

We might not be so lucky in 2018.

Being alarmed is not being alarmist -- it's being realistic. Trump's presidency has helped usher in unprecedented risks on numerous fronts.

Those 2018 Trumpian risks fall into three main categories: international security, American democracy and his dangerously unfit temperament. Let's take them one by one, using Trump's tweets -- from just a single crazy day -- as a disturbing vision of what may be in store this year.

Risk of war

First, Trump effectively threatened nuclear war with North Korea on Twitter, boasting that his "Nuclear Button" is bigger than Kim Jong-un's. Neither the United States nor North Korea has any strategic interest in a nuclear war that would leave millions dead. However, there is a rapidly growing risk of miscalculation as bluster between two ego-obsessed leaders ratchets up.

Foreign policy experts agree there is a serious risk of nuclear escalation on the Korean peninsula this year.

The highest risk of nuclear war since the Cuban missile crisis would present an overwhelming challenge for any seasoned and steady commander in chief. Trump is neither seasoned nor steady, but he does seem determined to create new international security risks outside of those (like North Korea) that he inherited.

Trump also tweeted more incendiary language toward the Palestinians, further provoking them after stunning the world by declaring Jerusalem as the capital of Israel in December.

And, while his tweets yesterday had reasonable language for dealing with Iran's nascent protests, his total lack of understanding of regional politics and his careless undermining of experts at the State Department do not bode well for managing a rapidly evolving situation that could quickly spiral out of control. The same is true for his tweet baiting of Pakistan.

Add that to the brutal war in Yemen and the ongoing slaughter in Syria. Cumulatively, despite Trump's genuine success in degrading ISIS in the region, the Middle East is one spark away from a destabilizing disaster with far-reaching consequences for American interests and global stability.

Most crucially, though, 2017 was the year that Trump started to dismantle the America-centric global order that presidents of both parties steadfastly built since World War II. Trump's "America First" tagline masks a foreign policy that has ended up putting China first because it aims to sharply reduce the role that the United States plays in the world.

Trump views long-term investments in allies as wasteful spending, and he sees the American-built system of global governance and trade as a series of "bad deals."

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In the process, confidence in American leadership from Obama to Trump has fallen 75% in Germany; 71% in South Korea; 70% in France; 57% in the UK; and 54% in Japan. As a result, 2018 will be a year that sees China's rise accelerate as a chasm of global leadership opens, according to a Pew survey.

When the tectonic plates of global power move, international security crises inevitably emerge from the gaps. 2018 will be no exception.

Threats to democracy

Second, Trump's tweets yesterday shine a light on how much he threatens democracy.

In a single day, he called to jail a political opponent without an indictment; insinuated that the former FBI Director James Comey should be locked up; suggested that his own Department of Justice was part of a "deep state" plot; attacked the press; and promised to unveil awards for the "most dishonest and corrupt media."

Any of these outbursts would be presidency-defining scandals for any normal president. Instead, they weren't really headline news because Trump's nuclear bluster was even more shocking.

It's plainly obvious that Trump has authoritarian instincts and impulses. 2018 could be the year that they finally have real impact as America sleepwalks into a constitutional crisis.

It's also obvious that Trump, if cornered by the system of checks and balances, would gladly tear down those democratic institutions rather than letting himself be subject to them. And increasingly Trump is cornered, as he faces Robert Mueller's criminal investigation and watches helplessly as his entourage gets picked off one by one by indictments.

In the meantime, Trump's staunchest Republican allies are engaged in a carefully crafted attempt to politicize rule of law and delegitimize any checks and balances that could contain Trump's most authoritarian desires.

A crisis moment

It's impossible to read Trump's tweets yesterday and think that the world's most powerful country is being led by a stable, rational individual. Aside from threatening nuclear war with a "my button is bigger than your button" childishness, Trump absurdly tried to claim credit for airplanes safely staying in the sky last year across the entire world.

And, eight of his tweets appear to have been in direct reply to Fox News programming -- suggesting that he spent most of his day watching television and responding to it.

Whether we like it or not, Trump's presidency is a crisis moment for democracy and international security. We somehow got away with it reasonably unscathed in 2017. A lot of that was sheer luck. I wouldn't bet on our luck lasting through 2018.