It has taken two years and one month, but Rajoy will finally make an official visit to the residence of the US President on Monday.
In the heavily scrutinized world of international diplomacy, such details can take on significance.
Spain's El Mundo pointed out on Monday that Barack Obama only waited 10 months after being elected to invite ex-President José Luis Rodríguez Zapatero. The daily also pointed out that the leaders of Greece and Italy hadn't had to wait so long to pay their respects to Obama.
But the Spanish Government said Rajoy's visit had been delayed by events including US elections in late 2012 and the arrival of a new US Ambassador in late 2013.
While bilateral relations between Spain and the US suffered a blow when Spain decided in 2004 to withdraw troops from Iraq, relations are now said to be on a firmer footing.
However, that relationship was threatened in late 2013 by revelations the US' National Security Agency spied on European allies including Spain.
That information, leaked by NSA whistleblower Edward Snowden, led to the US ambassador to Spain, James Costos, being summoned to explain the allegations at the Spanish foreign ministry.
In October, the Spanish newspaper El Mundo reported that US security services tracked 60.5 million telephone calls in Spain in a single month.
The article, co-authored by US journalist Glenn Greenwald, was based on previously secret documents obtained by Snowden, who is now living in temporary asylum in Russia.
But the head of Spain's own security agency later told the country's parliament that Spain had provided that data to the US as part of joint anti-terrorism efforts.
The White House said in a statement in December that Monday's talks would focus on a proposed US-EU trade pact, transatlantic issues and common security challenges in North Africa and the Middle East and elsewhere.
The meeting would also provide Prime Minister Rajoy with an opportunity to sell the success of Spain's economic reforms, Spain's El País newspaper reported on Monday.