Few votes at the UN General Assembly in recent years have been held in such an atmosphere of drama and tension as today's vote on the Trump administration's decision to recognize Jerusalem as capital of Israel.

The U.S., bracing for what is likely to be a near-unanimous rejection of its policy, took the highly undiplomatic step of warning other countries not to vote against it.

"As you consider your vote, I want you to know that the president and U.S. take this vote personally," U.S. Ambassador Nikki Haley said in a letter delivered to dozens of UN delegations, including Canada's. "The president will be watching this vote carefully and has requested I report back on those countries who voted against us. We will take note of each and every vote on this issue."

U.S. President Donald Trump doubled down on the threat at a cabinet meeting Wednesday. "They take hundreds of millions of dollars and even billions of dollars and then they vote against us," he said. "Well, we're watching those votes. Let 'em vote against us, we'll save a lot. We don't care."

That's generally the kind of provocation that gets people to tell you to go to hell. - Paul Heinbecker , former Canadian ambassador to the UN

Canada's former ambassador to the UN told CBC News the U.S. is likely to be opposed by a "very, very significant majority."

"I don't know what the numbers will be, and the United States will be putting a great deal of pressure on its allies but ... I think it's going to succeed only in isolating itself," said Paul Heinbecker, who served as ambassador under Jean Chrétien and also as chief foreign policy adviser to Brian Mulroney.

Heinbecker said the Haley letter won't help: "That's generally the kind of provocation that gets people to tell you to go to hell. And I suspect it will be in this case — especially since the person who's taking names is a president whose reputation internationally puts the United States' standing at the lowest ebb it's ever been."

It was Prime Minister Stephen Harper who changed the way Canada votes at the United Nations. His government's position was that there was too much focus at the UN on Israel's sins, driven by a large voting bloc of Arab and Muslim countries with an axe to grind against the Jewish state. In response, Canada would oppose all motions that "singled out" Israel for criticism.

Although it hasn't trumpeted its support for Israel as much as Harper did, the Trudeau government has followed the Harper line. It has frequently voted with the U.S., Israel and a small coterie of Pacific island nations, the largest of which, the Federated States of Micronesia, has a population smaller than Peterborough, Ont.

U.S. Ambassador to the United Nations Nikki Haley speaks during a UN Security Council meeting on the Middle East earlier this week. Haley and U.S. President Donald Trump have warned allies the U.S. is watching how they vote on today's Jerusalem motion. (Brendan McDermid/Reuters)

Last December, Britain, France, Germany, Italy, Russia, Japan, China and 162 other nations all supported a UN resolution reaffirming Geneva Convention protections to Palestinian civilians in the occupied territories. The Trudeau government joined forces with the U.S., Israel, Micronesia, Palau and the Marshall Islands to oppose it.

It also voted against motions calling on Israel to respect the "special international regime" status that Jerusalem has officially enjoyed since 1947, even though Canada voted to create that status and it remains part of Canada's official policy.

Canada under pressure

Two weeks ago, Canada voted against a UN resolution calling for a halt to the building of Israeli settlements in occupied East Jerusalem. The resolution passed 155-7. (Nauru, population 11,357, added its voice to the U.S. and Canada's on that vote.)

Canada's votes on Israel have drawn little public attention, and don't appear to have cost the Trudeau government support among Arab and Muslim voters, who may be more aware of Trudeau's support for Syrian refugees.

Under Prime Minister Justin Trudeau, Canada has continued the Harper government's practice of voting with the U.S. in opposing UN resolutions against Israel. (Adrian Wyld/Canadian Press)

But Heinbecker said it will be difficult this time for Canada to continue to vote under the radar against positions it officially espouses.

"The Canadian government will come under a lot of pressure and expectation to support the resolution along with its allies," he said.

"Nobody agrees with the Americans on this point."

He said U.S. allies would much prefer to be working together with the United States, not at cross purposes, "but this is an important point of principle."

Security Council seat could be at stake

Complicating matters further is Trudeau's desire to win a UN Security Council seat. The Harper government was widely believed to have blown its shot at a seat over its support for Israeli Prime Minister Benjamin Netanyahu. It could be embarrassing for Trudeau, who once excoriated Harper for that loss, to suffer the same rejection for the same reasons.

Heinbecker said any country that alienates a bloc of approximately 50 Muslim-majority nations is unlikely to gain the 129 votes generally needed to win a seat on the Security Council.

"You don't sacrifice a principle in order to get a Security Council seat," said the former diplomat. "But in this case, the principle is in the other direction. All the way back to the establishment of Israel, Canada has supported the idea of a two-state solution."

Trudeau is expected to come under pressure to step away from Israel's Prime Minister Benjamin Netanyahu and vote against the Trump administration's decision to recognize Jerusalem as capital of Israel. (Reuters)

The Trudeau government has also been careful not to alienate the Trump administration while NAFTA talks are under way. Nor would the Liberals want to lose support they have gained in the pro-Israel community.

A vote to support the Trump administration, on the other hand, would not only force Canada to again contradict its own longstanding positions, but would also risk alienating the party's pro-Palestinian supporters. And now, thanks to the Haley letter and Trump's comments yesterday, it would open the government to accusations that it caved to crude threats from Washington.

If Canada chooses the third option — abstention — the unintended consequence of Trump's Jerusalem move may be to cost the U.S.-Israel alliance its only voting ally with a population larger than the city of Peterborough.