Kiev’s Independence Square has been seized by protesters furious with Viktor Yanukovich, Ukraine’s president, because he has decided against signing a trade deal with the European Union — a deal that many ordinary citizens saw as critically important to their economic future. It is not immediately clear what Mr. Yanukovich can do, short of changing his mind and signing a deal. But the protests could well get bigger and more violent.

That is something that he, Russia and the European Union should do their utmost to prevent. President Vladimir Putin of Russia, who vigorously opposed such a deal because it threatened his own ties with Ukraine, may find satisfaction in winning this round. But he now has to come up with whatever he promised Mr. Yanukovich in return for rejecting the European Union deal, which presumably includes cheaper gas to help Ukrainians get through the winter. At the same time, he has to understand the message from Kiev’s streets: that Ukraine will not long be denied association with the European Union.

The West’s duty, meanwhile, is to give full support to the Ukrainians who are fighting for everything that an association with Europe represents to them: the commitment to democracy, the rule of law, honest government, human rights and a better future.

At the same time, the European Union, the United States and other Western democracies must appreciate certain realities. One of these is that Ukraine’s corrupt rulers and oligarch-dominated economy would have made for a difficult partnership. Proof of this is that Yulia Tymoshenko, the imprisoned former prime minister whose release was the one demand made by the European Union for signing the agreement, remains in prison. It is also important that the West appreciate that both Mr. Yanukovich and Mr. Putin fear that closer economic ties with Europe could cause short-term problems for their countries. Mr. Putin worries that such a deal could flood Russia with cheap goods; Mr. Yanukovich worries that he could provoke Mr. Putin into cutting off vital supplies of natural gas.