The real question is whether Mueller can pin evidence of a conspiracy on Trump. If the prosecutor can't reach Trump himself, some of Trump's Russia problems may begin to ease. If, however, it becomes clear the President or those near him have attempted to pervert the course of justice, then the situation will change abruptly. US political experts are virtually unanimous in their belief that Republicans will not impeach Trump in 2018, but that calculus may shift if the Democrats manage to capitalise on Republicans' unpopularity in the November mid-terms and take control of either the Senate or the House.
2. Will Trump or North Korea risk moving beyond bluster and posturing to military action?
In many ways, the likely trajectory of events surrounding North Korea is easier to predict. Based on events so far, it seems almost certain North Korean leader Kim Jong Un will continue to test increasingly powerful bombs and rockets. As Pyongyang's ability to strike the US mainland increases, Washington will get increasingly aggressive — but likely will still remain reluctant to launch any kind of strike that could trigger a devastating conflagration.
There remain several wildcards in play, however. The most obvious is whether Trump might ignore the cautionary noises coming from the Pentagon and beyond and attempt to decapitate Kim's regime and weapons programme militarily.
For now, both Japan and South Korea remain extremely cautious about the idea of a unilateral US strike, with South Korea repeatedly stating that it would wish to veto any such action.
Washington's longstanding alliance with South Korea means that Trump should — in theory, at least — get Seoul's consent before trying to shoot down a North Korean test missile using regional ground-based interceptors. Such a strategy would be high-risk — Washington's credibility would suffer if the interceptor rocket missed its target.
Aside from the nuclear threat, don't discount Pyongyang's growing cyber capabilities. Its suspected efforts to penetrate the US electric grid could escalate into crippling attacks on critical infrastructure.
Keep an eye on Russia and China too. So far, Moscow has been broadly supportive of Pyongyang's nuclear ambitions while Beijing has been much more cautious. A shift in either position might well influence Kim's thinking.
Whatever happens, expect more posturing and more sanctions.
3. Will Europe's multiple crises reach crunch point?
This has been a volatile year for Europe. After the shock of the Brexit vote in 2016, France and the Netherlands fended off electoral challenges from the far-right.
However, Chancellor Angela Merkel emerged from Germany's October election with diminished support and a struggle to form a viable coalition government. That means the country may have to go back to the polls next year.
The surprisingly strong performance of pro-Catalan independence parties in elections this month means domestic tensions within Spain will remain on the table next year, with a new independence referendum looking increasingly likely.
The problem is none of the strains within the continent have gone away — frustration with government policies on migration, the ongoing struggle to keep the single currency bloc and, of course, the ongoing trauma of how to make Brexit work.
The latter issue will escalate in importance throughout the year, as British and European Union negotiators attempt to transform this month's preliminary agreement into a workable deal before Britain leaves the union in March 2019. That progress will inevitably hit problems, and if it breaks down entirely a new British election — or even another referendum — remain plausible.
The far-right hasn't gone away either. The results of local and national elections in Belgium, the Czech Republic, Holland, Finland, Hungary, Ireland, Italy and Sweden will all be watched for signs that populists are gaining ground.
4. Will new conflicts erupt as US influence in the Middle East slips?
For all the sound and fury following Trump's decision to move the US Embassy in Israel from Tel Aviv to Jerusalem, 2018 will likely see US ever less at the heart of events in the region.
US forces will continue to mop up remnants of Isis (Islamic State) and other militant groups, but Washington will increasingly take a backseat to regional heavyweights Saudi Arabia and Iran when it comes to driving events. With Tehran seeming to have strengthened its influence in Iraq and Syria this year, expect Sunni Saudi Arabia and its Gulf allies to push back ever harder against their Shia rival.
The war in Yemen will likely remain the bloodiest theatre, a humanitarian catastrophe largely invisible from the outside world. In addition, some analysts already believe Riyadh is already quietly encouraging Israel to consider another war in Lebanon to push back Iran's Hizbollah proxies.
Another story worth watching will be the push by Kurdish groups for great influence within Turkey, Syria and particularly Iraq, where strains have become particularly severe since September's independence referendum.
5. Will 2018 see growing challenges to authority in Russia and China?
On balance, 2017 was a good year for the leaders in Moscow and Beijing. While the West remained mired in domestic clinical crisis, Chinese President Xi Jinping and Russia's Vladimir Putin have never looked more in control.
Beneath the surface, however, those assumptions are already being tested. Russia saw a string of anti-government and anti-corruption protests throughout the year, and Putin will no doubt be hoping to avoid a repeat next year of one of the few prospects that could complicate the presidential election he seems certain to win. Turnout may be reduced, however — challenger and anti-corruption campaign Alexei Navalny called for a boycott this week after he was banned from running against Putin.
In China, Xi secured his position as the most powerful Chinese leader since Mao at the quinquennial Communist Party Congress in September. There too, however, there are signs of quietly mounting discontent and protest, particularly in Hong Kong.
Don't expect either country to see seismic change next year on the back of these trends. But they are worth watching, for they may point to much more significant things to come.
