It didn't take long for the most visible signs of Justin Trudeau's visit to Washington to disappear. The hashtag #Trubama stopped trending on Twitter. Down came the Canadian flags that lined Pennsylvania Avenue.

President Barack Obama returned quickly to the business of finding a nominee for the U.S. Supreme Court. Based on the howls of outrage from Republicans who control Congress, his choice — whenever he makes it — has little to no chance of being confirmed before he leaves office.

The Trudeau visit, with all its overtones of friendship, partnership and cooperation, must have been a welcome relief, brief as it was.

And the U.S. news networks that covered the Trudeau-Obama news conference Thursday returned to the race to replace the president… a kind of newscast soap opera carefully alternating between Hillary Clinton and Donald Trump as they close in on their respective nominations.

"The U.S. only gives you a narrow window of time," says Laura Dawson, director of the Canada Institute at the Woodrow Wilson Center in Washington.

"That window is open for two days, it's a 'give us your best shot' window and then we're on to other things."

Dawson says Trudeau made the most of the opportunity, despite what she feels was a mistake trying to oversell the deals that would come out of the three-day visit: on climate change and adding more locations where Canadian and other travellers can pre-clear U.S. customs before heading south of the border.

However, the most important work may not have been done at the White House at all, but rather at the other end of Pennsylvania Avenue, where Trudeau met with both Democrats and Republicans on Capitol Hill.

Dawson says it's obvious Trudeau appeals to progressives in America. But in a presidential election year, his message needs to reach constituencies that have less in common with him, less interest in what's he's offering on the policy front.

"I think the real task for this visit was to reach out to a broader base of Americans, to a more Conservative America, to say, 'Canada is here, we are open for business. We're your partners and we will work with whoever is running the United States next.'"

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Canadian Prime Minister Justin Trudeau speaks at the Global Progress luncheon sponsored by the Center for American Progress March 11, 2016 in Washington, D.C. (Win McNamee/Getty Images)

New challenges ahead

Whoever that is — Republican or Democrat, Trump or Canadian-born Ted Cruz, Hillary Clinton or Bernie Sanders — the next president poses a new set of challenges for a Canadian prime minister keen to re-establish close ties in Washington.

Clinton isn't keen on the Trans-Pacific Partnership, the Pacific Rim trade deal that includes both Canada and the U.S. Sanders would rip of NAFTA. Trump doesn't much like NAFTA either, and Cruz? Well, he renounced his Canadian citizenship in 2014. Canada's still not a happy topic.

Put it all together and Canadian interests continue to face serious challenges in the U.S.

Pelosi greets Trudeau on Capitol Hill1:22

Start with softwood lumber. The deal that ended punishing tariffs against Canadian softwood exports has expired. A new one needs to be be reached before October or American producers will have another opportunity to go after Canadian producers again.

Obama and Trudeau have directed their trade officials to explore options for a solution and to report back within 100 days "on the key features that would address this issue."

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Prime Minister Justin Trudeau, centre, poses for a photo with Senate Majority Whip John Cornyn (Rep.) of Texas, left, and Senate Minority Leader Harry Reid (Dem.) of Nev., before a meeting on Capitol Hill Thursday. (Cliff Owen/Associated Press)

Trudeau tapped Trade Minister Chrystia Freeland for the task, and while she says the close working relationship between the leaders will lead to results on this and other contentious bilateral issues, Congress can't be ignored.

"One of the things which I think may be a little bit less noticeable than the glamorous state dinner was the opportunity that we had to spend time with senators, to spend time with Congressmen and women," Freeland told CBC Radio's The House in a separate interview airing Saturday.

"These are important conversations and are going to be the basis of a lot of specific deals being done and irritants being resolved."

Even that window is narrow as members of the House and many Senators are also seeking re-election this year.

Highlights from Justin Trudeau's welcome to the White House5:01

Getting noticed is hard enough.

But many Republicans see no benefit in supporting anything Barack Obama has to offer out of this visit, let alone a climate-change deal with Canada or the mere suggestion of making it easier for people to move back and forth across the northern border. Democrats have a history of campaigning to protect American jobs. In northern states, it's not a bad vote-getter.

So paying attention to Congress might not land Trudeau on the front page of major American dailies as his official visit did this week. It might not get him on a single newscast.

But in the long run, it might land Canada what it wants most of all when this U.S. election season is over: co-operation on priorities the Trudeau Liberals share now with a president who will no longer be around.

American attitude towards Trudeau10:01