If re-elected as president in November 2020, Donald Trump will undoubtedly continue to pursue in his second term the same foreign policies that he has been pursuing in his first. His re-election, though, could have an extremely disruptive effect on U.S. relations with its traditional Western and other democratic allies.

Many of these, of course, already oppose Trump’s foreign policies, including his undercutting of NATO, pulling out of globally-backed international agreements such as the Paris Climate Agreement and the Iranian nuclear accord (and sanctioning U.S. allies if they adhere to its provision of providing economic relief to Iran), and most recently, halting U.S. funding for the World Health Organization.

Yet despite how many of them have found Trump’s foreign policies to be harmful to their own interests and ideals, the U.S.’s democratic allies have sought to maintain good relations with Washington, and Trump himself, presumably based on the belief that his 2016 election was a fluke, that the American people would surely not re-elect him in 2020 after seeing how poor a leader he has been, and that the next president — whether Democrat or Republican — would be a moderate who would revive the U.S.’s traditional foreign policy approach of valuing and supporting its democratic allies in particular.

For while the re-election of Trump will not serve to worsen allied perceptions of him, it could well serve to undermine their faith in both the reliability and utility of the United States, and even Americans themselves, as allies. This is because while the U.S.’s allies may hope or believe that a sufficient number of those who voted for Trump in 2016 now regret having done so, their re-electing him in 2020 with the full knowledge of his mercurial nature and ill-advised policies would mean that the judgment of American voters (even if not the majority of them, as in 2016) who willingly re-elect Trump in 2020 raises the specter that they might elect someone like him in subsequent elections. If they come to believe that Trumpism might well be a permanent feature of American foreign policy going forward, then they must fundamentally reassess their relations with the U.S.

In other words, if the U.S.’s principal democratic allies lose hope that the U.S. will “return to normal” because Trump is re-elected, they may more actively seek to limit the damage to their own interests from his pursuit of policies they deem harmful.

German Chancellor Angela Merkel raised this possibility in late May 2017 when, after Trump demanded at a NATO summit that other members pay more while refusing to reiterate the U.S. commitment to the NATO Treaty’s mutual defense clause (Article 5).  “The times in which we could completely depend on others are on the way out. I've experienced that in the last few days,” she said then.

More recently, Nathalie Tocci, director of Italy’s influential Istituto Affari Internazionali, wrote, “As strategic competition between the U.S. and China continues to heat up, the EU must redouble its quest for autonomy, so that it can triangulate between the two rather than being forced to choose between them or to bow to one of them.”

In other words, while the U.S.’s traditional democratic allies are not likely to renounce their alliances with the U.S. if Trump is re-elected, their doubts about not just Trump’s but the American public’s commitment to their defense and well-being may lead them to conclude that they must increasingly look out for themselves.

Unfortunately, many of them may conclude that they must do so through accommodating either or both of the two authoritarian great powers, Russia and China. (The U.S., of course, has several authoritarian as well as authoritarian-leaning elected allies that support Trump, but most of these already have developed cooperative ties with Russia and China.)

While it is true that the European Union — with its large population and economic capacity to build a self-sufficient defense capability — could theoretically become a great power in its own right (as some Europeans have advocated), its divisions as well as its unwillingness to sacrifice its generous welfare benefits in order to increase defense spending make this unlikely to occur any time soon.

Instead, some European governments may respond to the combination of decreased American reliability as an ally and increased assertive Russian behavior through seeking to appease Moscow.

Others may hope that cooperating with China may be a way to induce Beijing to restrain Moscow. By contrast, some of the U.S.’s Asian allies — Japan and South Korea in particular — may try the opposite policy of seeking increased cooperation with Russia in order to contain China.

The U.S.’s authoritarian allies in the Middle East and elsewhere may seek to cooperate with both Russia and China against their regional adversaries. All of them may be hoping to take advantage of a Sino-Russian rivalry that might not actually emerge.

Yet even if it does, U.S. allies that come to further doubt the U.S.’s reliability due to the re-election of Trump may end up working at cross purposes in largely uncoordinated hedging operations which render them ineffective.

But even if Trump loses the election this year, rebuilding relations with the U.S.’s traditional allies is going to take considerable time and effort after the damage Trump has caused.