Anti-Israel organizations across the globe began holding “Nakba Day” events this past weekend—heralding the “catastrophe” that Palestinians call the creation of modern-day Israel in 1948. The largest took place in London: Some 3,000 people marched in the British capital under the banner: “Liberate Palestine.”

The leader of the march, Ahed Tamimi (the provocateur who assaulted an Israeli soldier last year) didn’t bother hiding what exactly they intend to liberate: “From the [Mediterranean] Sea to the [Jordan] River, Palestine will be free,” she shouted in cadence—with fellow marchers repeating in unison her calls to eradicate Israel.

The march, this time around, received the full support of British Labour Party leader Jeremy Corbyn. The message of support he issued could easily have been mistaken for a statement from a Hamas spokesman. In it, he accused Israel of violating human rights, shooting at innocent protesters and preventing justice. What about the barrage of nearly 700 rockets fired by Palestinian terrorist organizations at Israeli civilians just last week?

Corbyn, apparently, isn’t aware of that minor, tedious detail, or just prefers to ignore it.

The problem is that Corbyn, who has drifted farther than any other European politician into open and utterly illogical support for Israel’s enemies, could still become prime minister of Great Britain. Under his leadership, the winds of hate have swept through his party. The situation has reached the point where, during the march in London, 119 Labour lawmakers who belong to a pro-Israel lobby were denounced as a “fifth column.”

As for members of Hezbollah and Hamas, Corbyn refers to them as “friends fighting for peace, understanding and dialogue.”

In addition to terrorists, Corbyn also counts among his friends Britain’s most notorious anti-Semites and Holocaust-deniers, some of whom have even infiltrated Labour’s ranks under his leadership. Corbyn’s hatred for Israel is so unbridled that he can’t help but do the inexplicable, such as visit the grave of one of the PLO terrorists who butchered the Israeli athletes at the 1972 Munich Olympics.

His inelegance and moral blindness essentially reveal the true face of a large camp within the British and European left. His support for the Arab murderers is accompanied by calls to boycott Israel and anti-Semitic intimations towards Jews not only in Great Britain, but in general.

As we recently witnessed, Corbyn penned a glowing forward for a book claiming that Jews control the global financial system. It appears that of all the anti-Semitic libels, the only one he hasn’t yet parroted is that Jews make their Passover matzah using the blood of Christian children. But who knows? Maybe we just need to be patient.

Corbyn’s fanaticism has indeed pushed the Conservative Party to increase its support for Israel, but the instability in the country in the wake of the Brexit referendum poses a real threat to the Conservative Party’s power. Israel must start preparing for the possibility of Corbyn becoming prime minister with the help of two precedents from the not-so-distant past.

At least twice, when anti-Semitic leaders were elected to the highest post in Austria (Kurt Waldheim in 1986 and Jörg Haider in 2000), Israel downgraded diplomatic ties and spearheaded an international campaign to label both these individuals personae non grata. Corbyn is no different than Waldheim and Haider; in many ways, he is worse and more dangerous. Therefore, Israel would do well to signal, starting now, that if he becomes prime minister Great Britain will become patriam (country) non grata.

Ariel Bolstein is the founder of the Israel-advocacy organization Faces of Israel.

This column first appeared on Israel Hayom.