Donald Trump has started 2019 locked in a fierce political battle with new House Speaker Nancy Pelosi, a fight he will lose.
He can't force Democrats to apportion money for a wall between the United States and Mexico, but influential conservatives in media threaten to punish him if he retreats. He'll eventually find a way to surrender while declaring victory. And then his year will become even more complicated.
Trump's 2019 "to-do" list is formidable. He must help restore confidence in the US economy after three months of the worst US stock market meltdown in many years, and he must accomplish this at a time when global economic growth is beginning to look soft.
He must reassure the world that the US and China are not on a course towards endless trade conflict or a Cold War-scale military confrontation while addressing the genuine security concerns of those who believe China continues to take advantage of the US, its companies, and its workers.
He will need to show real progress toward denuclearisation of the Korean Peninsula by persuading North Korean leader Kim Jong Un that he can't get something for nothing. He must persuade critics that the vague promises made last year in Singapore hold promise without allowing Kim to continue with clandestine nuclear development.
He needs to deliver the promised withdrawal of US troops from Syria without appearing to cede power and influence in the Middle East to Russia and Iran - and without leaving Kurds and other allies at the mercy of Turkey's president and his military. Trump must execute this retreat without losing whatever confidence the US Defence Department still has in his leadership.
He must begin to prepare for re-election. With low approval ratings, growing doubts among his core supporters, and after a loss of historic scale in November's Midterm elections, he must discourage any Republican from challenging him for the party's nomination, and he must find a way to break the momentum that Democrats now enjoy.
The obstacles he faces are daunting. China's Xi Jinping can't be seen to buckle under Trump's pressure, and China's political and economic system gives the Chinese leader formidable weapons with which to limit damage to China's economy. Russia's Vladimir Putin can treat Trump as a compromised figure, and Europeans who have long called for less reliance on US protections now have the best case they've ever had. The cost of partnership with Trump is rising for leaders of countries who can afford to ignore him, and an "America First" foreign policy driven by Trump's capricious personality makes the benefits less clear.
On the domestic front, Trump was elected in part because he had no experience in government. In that sense, he was the embodiment of change. The downside for Trump is that he is still unsure how government actually works. Nancy Pelosi is as experienced, savvy, and ruthless an adversary as the President could expect to face.
The party Pelosi leads has real power for the first time since Trump was elected, and Democrats intend to use it to subject him to a level of scrutiny Trump has never experienced. They will subpoena both documents and members of his Administration to testify under oath on any number of sensitive subjects, and Trump's patience, poise, and self-confidence will be tested. Special Counsel Robert Mueller will continue to probe nearly every aspect of Trump's public life. Whether weeks or months away, the report of his findings will shake Washington like nothing we've seen in a generation.
The greatest risk for Trump is that Republicans - voters and lawmakers - decide they can no longer afford his leadership. The daily "outrages" reported by the press and repeated by incredulous Democrats won't sway Trump's most loyal supporters or their elected representatives. But if Trump comes to be seen as a loser - because foreign leaders are ignoring him, Democrats are thwarting his plans, the economy is turning, and especially if polls begin to signal he can't win - there is a risk they will abandon him.
We're still some distance from that point. Those who underestimate Trump's political instincts are making a mistake. There have been few figures in American public life who better understand the sources of fear and anger that drive his most reliable followers, and Democrats may nominate a presidential candidate that pushes Republicans back towards Trump.
But 2019 is sure to be the most challenging year of Trump's life.
• Ian Bremmer is the president of Eurasia Group and author of Us vs Them: The Failure of Globalism.