There's a reason Trudeau's Washington visit starts at the Capitol

It's inevitable that when a Canadian prime minister visits Washington, the trip to the White House generates the most attention — a reality of cross-border politics as enduring as the recycling of quotes from JFK and old jokes about mice sleeping with elephants.

That tradition continues this week, with Prime Minister Justin Trudeau in Washington for a two-day visit culminating in meetings Thursday with the presidents of the United States and Mexico.

But this time, one of the most important stories in continental relations might be unfolding elsewhere, a day early, a dozen blocks east of the White House.

Trudeau will be on Capitol Hill on Wednesday meeting with congressional leaders in both the Senate and House of Representatives.

Democrats there are putting the finishing touches on a massive piece of legislation with both domestic and international implications — a nearly $2 trillion US bill that is the most important legislative act of Joe Biden's presidency.

One element in particular has Canadian policy-makers terrified: a tax credit for electric vehicles that favours cars assembled in the U.S., prompting warnings from Ottawa of lost jobs, disrupted supply chains and a retreat from six decades of co-operation in auto production.

It's no accident that Biden will be in Detroit on Wednesday; he'll be promoting his agenda at a General Motors electric-vehicle plant that would benefit from the credit.

Politicians from Canada and elsewhere have been pleading with their American counterparts to either drop or modify the plan, arguing it violates trade agreements and could prompt trade cases.

And the key American to convince doesn't necessarily work in the White House. The destiny of this bill could be decided by another Joe, who works on the other end of Pennsylvania Avenue.

Sen. Joe Manchin of West Virginia is regarded as the 50th and final vote that Democrats need to pass a budget bill in the Senate — and he's been wavering on parts of it.

There's a reason he attracts a media mob of congressional reporters who trail him and make note of his every utterance on the bill. After all, he may decide the fate of legislation whose multi-year price tag exceeds Canada's entire annual gross domestic product.

He's among the rare holdouts who have watered down the bill's provisions on climate policy, family assistance and health care.

The electric vehicle tax incentive is arguably the most important climate policy left standing in the bill, and last week Manchin made clear he doesn't like it.

He's spoken at length with Canadian Ambassador Kirsten Hillman about the policy and has never quite laid his cards on the table about what he wants next.