Parties can be a good measure of friendship.

For years, the Christmas party at the U.S. ambassador's home was a lovely affair, but not frequented by many Conservatives from Stephen Harper's cabinet.

That all changed last December.

The U.S. Ambassador to Canada, Bruce Heyman, could barely contain his excitement as everywhere you turned, there was yet another minister from Justin Trudeau's newly named cabinet being swarmed by invitees anxious for face time.

To say nothing of the appearance of the prime minister himself, who was generally mobbed by guests.

Just catching my breath. An amazing evening. So many incredible friends. Thank you <a href="https://twitter.com/hashtag/Canada?src=hash">#Canada</a> <a href="https://twitter.com/hashtag/cdnpoli?src=hash">#cdnpoli</a> <a href="https://twitter.com/JustinTrudeau">@JustinTrudeau</a> <a href="https://t.co/X9AaiGsxiE">pic.twitter.com/X9AaiGsxiE</a> —@BruceAHeyman

That party marked the beginning of warming relations between the U.S. and Canada.

This week's state visit is the very public display of it.

The goal will be to show Canadians and Americans this relationship isn't just about two leaders who get along, but rather two countries whose ties run deep.

Chrystia Freeland, Trudeau's minister of international trade and the chair of the cabinet committee on Canada-U.S. relations, says this is as much about human relations as anything else.

"The relationship between Canada and the United States is the most successful economic, political and strategic relationship in the world. Our biggest trading partner, the largest undefended border," she told CBC News.

"This is the first state visit in 19 years, and it is a hugely important opportunity to renew those ties and make them even closer — and for the prime minister and the president to work together on shared priorities, particularly climate change."

Rosemary Barton, host of CBC News Network's Power & Politics takes us on a tour of Canada/US state dinners 1:12

Pipelines blocked progress?

That isn't to say there was no working relationship between Stephen Harper's Conservatives and the Obama administration.

It was, after all, under Harper that the two countries signed the Beyond the Border pact in 2011 in an attempt to ease security and trade at the world's longest shared common border.

More progress is expected to be made on implementing some key parts of that deal this week during the state visit, specifically dealing with the entry and exit initiative that Canada has been reluctant to implement fully due to privacy concerns around information sharing.

So progress was made under the Conservatives on some files.

But other issues seemed to take up a lot of space, perhaps to the detriment of the relationship — the construction of the now-rejected Keystone XL pipeline being the most obvious.

Former prime minister Stephen Harper, seen here in a private meeting with U.S. President Barack Obama on the margins of the 2011 APEC Summit in Hawaii, criticized the Obama administration publicly and struggled to make progress on Canada's cross-border agenda. (Sean Kilpatrick/Canadian Press)

Prime minister Harper seemed to believe taking a tough line on the issue was the only way forward.

Clearly running out of patience as the file lingered in the United States, Harper proclaimed in 2013 that "you don't take no for an answer" and that the project was a "no brainer."

Perhaps the rhetoric was warranted. Certainly it was not these bold declarations that sealed the fate of the pipeline, but the brash language did nothing to help foster a stronger relationship between either leaders or governments.

Mulroney-Reagan relationship iconic

Other prime ministers seem to have had a better understanding of the end game. Two of them have been afforded two state visits apiece: Pierre Trudeau and Brian Mulroney.

It is perhaps Mulroney's relationship with the United States, and then president Ronald Reagan in particular, that has become an iconic symbol of what is possible.

The Shamrock Summit in Quebec City in March 1985 featured the two leaders singing When Irish Eyes are Smiling on stage in a tribute to their shared Irish heritage, but so much more was happening behind the scenes to build the relationship and to make progress on the acid rain treaty that would finally be signed in 1991.

In U.S. security council documents released in 1999, it was clear that bonhomie was viewed as a turning point in relations.

Then secretary of state George Schultz said of Mulroney in a unclassified memo, "We are ideologically on the same wavelength."

In a March, 2012 speech to mark the anniversary of the acid rain treaty, Mulroney made it clear Canada's influence in the United States was built first and foremost on his deep friendships with both Reagan and later George H.W. Bush.

He also warned in the same speech of the dangers of not nurturing that relationship: "It is amusing to note that, in some Canadian quarters, friendly relations with the president of the U.S. are viewed with scorn and alarm. A relationship that leaders of others nations would treasure is derided by these same critics — supercilious and uninformed as they are — as subordination, unworthy of an independent nation."

The Mulroneys and Reagans were close personal friends as well as strategic political allies. Brian Mulroney spoke at Reagan's 2004 funeral. Here, Mila Mulroney, left, gets a kiss from U.S. President Ronald Reagan as his wife, Nancy, gets a kiss from then prime minister Mulroney, right, a Toronto economic summit in 1988. (Ron Poling/Canadian Press)

If Mulroney's tenure as prime minister is any evidence, it would seem friendship can get results: not just the acid rain treaty, but the Canada-U.S. free trade deal, the North American free trade deal and an agreement on Arctic sovereignty all marked Mulroney's time as prime minister.

Even if this president is not around for much longer, in the coming days Trudeau will be seen by the rest of the world as a leader deserving not only of a fancy party, but of a strong and trusted friendship that may ultimately lead to big results.