US President Donald Trump’s fickleness and unpredictability are sometimes touted as a useful foreign policy tool to keep authoritarian leaders such as North Korea’s Kim Jong-Un, China’s Xi Jinping and Russia’s Vladimir Putin off guard. None of them can know for sure what the US president is capable of doing. Will he launch a missile strike, impose sanctions or trade restrictions in a sudden fit of anger? Bullies and strongmen are left apprehensively guessing what his next move will be. They are likely to think twice before crossing Trump.But what can be seen as an asset with regard to America’s enemies, can work in a converse direction with allies. Israel, the Kurds, Saudi Arabia and other American allies were led to believe by US military and foreign policy officials that America would remain in Syria as part of a broad campaign to contain Iran’s disruptive influence there.Now Trump is telling them to fend for themselves.We will have as of three months ago $7 trillion in the Middle East over the last 17 years, Trump said at the White House on Tuesday. “We get nothing, nothing out it... we have nothing except death and destruction. So I want to get back to building America.”He was reiterating comments he made Thursday before a crowd of union builders in Richfield, Ohio, in which he said he would be pulling US troops out of Syria “very soon.”If Trump’s latest statements do indeed mark a real change in policy in the Middle East and are not just an impulsive throwaway, it will have a number of adverse consequences, both for Israel and for other US allies in the region.For Israel, a US retreat increases the chances of a direct confrontation with Iran. The Islamic Republic insists on capitalizing on the blood and treasure it expended during the years it propped up Bashar Assad’s regime and established a permanent military presence in Syria. Israel, in contrast, cannot, and will not, accept Iranian military bases on its northern border. If the US does nothing to prevent this, Israel will be forced to react. As Prime Minister Benjamin Netanyahu said during his speech to AIPAC in March, “We must stop Iran. We will stop Iran.”According to Amos Yadlin, head of the Institute for National Security Studies in Tel Aviv, Tehran wants to renew Assad’s arsenal of longrange missiles, most of which were used or destroyed during the civil war. It also wants to build missile production facilities on Israel’s border.The idea is for Iran to create a double missile threat, from both Syria and Lebanon, with more accurate and longer-range missiles. Eventually, when the sunset clauses in the Iran nuclear deal take effect, Iran could augment this missile threat with nuclear warheads.Well before this happens, Israel would have no choice but to defend itself.A US retreat would also be a disaster for democracy promotion. Kurds, Arabs and other groups that make up the Syrian Democratic Forces were the US’s most important allies in the fight against Islamic State. Without continued US support, however, areas of eastern Syria that were liberated from ISIS will once again fall into the hands of anti-democratic forces, this time Turkey, Iran and the Assad regime.More important, however, a US retreat would send out a problematic message to potential future US allies seeking to overturn autocratic regimes in the Middle East and elsewhere: the US is a fickle power that cannot be trusted.This is precisely the message anti-democratic autocrats in North Korea, China, Russia, Turkey and Iran would like to broadcast to their feeble opposition groups. They want to make it clear that democratic forces are a losing cause and the US is an unreliable power that will turn on its allies.Thankfully, Israel is a stable, democratic nation with the strongest military in the Middle East and a robust economy. It has never asked the US to fight its battles. Other fledgling democratic forces in the region are, unfortunately, in a much more fragile position and are in need of US help. History has taught that the US cannot escape confrontation by escaping into isolationism. Doing so only postpones the inevitable conflict and makes things worse.