When Klaus Iohannis smiled for cameras alongside Donald Trump on Tuesday, the Romanian president became the 10th European leader to visit the president at the White House this year.

But none have come from the large Western European powers that have been cornerstone US allies for decades. Instead, Mr Trump has courted and been courted by Central and Eastern European leaders.

For Mr Trump, the region offers the potential for new trade, energy and military arrangements that can sometimes circumvent Western Europe and tweak traditional leaders, such as Angela Merkel.

"We have a great relationship. We have a big trade business going on," Mr Trump said at the start of his Oval Office meeting with Mr Iohannis. "We buy, they buy."

Before the meeting, a senior administration official said Mr Trump is highlighting "the importance of Central Europe to the United States, both as allies and security partners, and as business and commercial partners for the future," a senior administration official said on Monday.

President Trump in Britain for state visit: In pictures Show all 40 1 /40 President Trump in Britain for state visit: In pictures President Trump in Britain for state visit: In pictures President Trump, Prime Minister Theresa May and Jeremy Hunt, the foreign secretary, pose for a photo during dinner at Winfield House, the US ambassador's residence in London AFP/Getty President Trump in Britain for state visit: In pictures President Trump and Prime Minister Theresa May share a laugh outside of Downing Street Reuters President Trump in Britain for state visit: In pictures President Trump walks with the Queen while other guests follow as they arrive at a state banquet in Buckingham Palace AFP/Getty President Trump in Britain for state visit: In pictures The red carpet is rolled out in front of Downing Street prior to the arrival of President Trump AP President Trump in Britain for state visit: In pictures President Trump meets with prime minister Theresa May for a business roundtable meeting at St James' Palace in London AP President Trump in Britain for state visit: In pictures President Trump makes a speech at the state banquet in Buckingham Palace Getty President Trump in Britain for state visit: In pictures President Trump and the Queen share a toast at the state banquet in Buckingham Palace Reuters President Trump in Britain for state visit: In pictures Philip May and Melania Trump attend a garden party for families of Downing Street staff on the second day of President Trump's visit Getty President Trump in Britain for state visit: In pictures President Trump meets with the Queen at Buckingham Palace as he arrives on the first day of his three-day state visit PA President Trump in Britain for state visit: In pictures A mixed crowd of supporters and detractors waits outside Buckingham Palace ahead of the arrival of President Trump Reuters President Trump in Britain for state visit: In pictures President Trump and the Queen view an exhibition of items from the Royal Collection that are of historical significance to the US PA President Trump in Britain for state visit: In pictures President Trump inspects an honour guard during a welcome ceremony in the garden of Buckingham Palace AP President Trump in Britain for state visit: In pictures The police block a road leading to Westminster Abbey, where Donald Trump is visiting on the first day of his state visit PA President Trump in Britain for state visit: In pictures President Trump walks with Prince Charles in the gardens of Buckingham Palace AFP/Getty President Trump in Britain for state visit: In pictures The McDonalds restaurant on Whitehall near to Westminster Abbey provides an excuse as to why they are not serving milkshakes today, though many have speculated that it is due to the recent trend of pouring milkshakes over right wing political figures Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures Protesters with anti-Trump signs stand on Whitehall near Downing Street Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures President Trump and First Lady Melania are welcomed by the Queen, Prince Charles and Camilla at Buckingham Palace EPA President Trump in Britain for state visit: In pictures King's Troop Royal Horse Artillery perform a gun salute to honour President Trump's state visit and to mark the 66th anniversary of Queen Elizabeth's coronation at Green Park Getty President Trump in Britain for state visit: In pictures A protester stands on Whitehall near Downing Street holding a sign with an anti-Trump message Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures A supporter welcomes the president's visit on Whitehall near Downing Street Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures A miniature Trump balloon in the protest on Whitehall near Downing Street Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures A protester wears a "No Trumps" card in his hat as he walks nearby to Buckingham Palace Getty President Trump in Britain for state visit: In pictures President Trump walks with Prince Charles and a Buckingham Palace guard as he is welcomed on the first day of his three-day state visit AFP/Getty President Trump in Britain for state visit: In pictures Dedicated pro-Trump and pro-Brexit campaigner Joseph Afrane awaits the president's arrival at Buckingham Palace Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures Crowds watch as Marine One, the helicopter carrying President Trump, arrives at Buckingham Palace PA President Trump in Britain for state visit: In pictures President Trump and First Lady Melania depart from Air Force one at Stansted Airport Reuters President Trump in Britain for state visit: In pictures Supporters of the president - and detractors of London mayor Sadiq Khan - await his arrival at Buckingham Palace Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures President Donald Trump salutes an honour guard as he and first lady Melania Trump arrive at Stansted Airport AP President Trump in Britain for state visit: In pictures President Trump and First Lady Melania arrive at Winfield House, the US ambassadors residence in London AP President Trump in Britain for state visit: In pictures An anti-Trump protester awaits the president's arrival at Buckingham Palace Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures Dedicated pro-Trump and pro-Brexit campaigner Joseph Afrane awaits the president's arrival at Buckingham Palace Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures A protester mowed this message into a field nearby to Stansted Airport Born Eco President Trump in Britain for state visit: In pictures An anti-Trump protester awaits the president's arrival at Buckingham Palace Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures A marching band parades down the Mall in front of Buckingham Palace ahead of the arrival of President Trump Reuters President Trump in Britain for state visit: In pictures Supporters of the president await his arrival at Buckingham Palace Tom Batchelor / The Independent President Trump in Britain for state visit: In pictures President Trump shakes hands with Jeremy Hunt, the foreign secretary Sky News President Trump in Britain for state visit: In pictures A policeman stands on the Mall, one of the roads leading to Buckingham Palace that is closed for the president's visit Reuters President Trump in Britain for state visit: In pictures Air Force One lands carrying U.S. President Donald Trump and First Lady Melania Trump arriving for their state visit to Britain Reuters President Trump in Britain for state visit: In pictures An honour guard await Trump's departure from Air Force One at Stansted Airport Sky News President Trump in Britain for state visit: In pictures President Trump and First Lady Melania depart from Air Force one at Stansted Airport AP

The president has met with the leaders of Austria, the Czech Republic, Slovakia, Turkey, Hungary and Poland. Mr Iohannis will be the seventh from Central or Eastern Europe.

He has also welcomed the leaders of Switzerland, Ireland and the Netherlands in Europe, as well as leaders from Canada, the Middle East, South America, East Asia and South Asia.

Mr Iohannis, who also visited in 2017, praised Mr Trump and what he called the "right path" of relations.

"We have the opportunity to talk about our very good strategic partnership, and under your strong leadership we progressed, and we will continue doing so," Mr Iohannis said as Mr Trump looked on approvingly.

Mr Trump also gave Mr Iohannis a plug as he heads to elections this fall, saying he thinks the Romanian leader will "do very well."

The trip was timed in part to seek Mr Trump's blessing, seeing it as a political boon.

"Some of the Eastern European leaders, whether Hungary, the Poles, and now Romania, have basically figured out how to deal with Trump, and they appeal to some of his more illiberal instincts," said Kelly Magsamen, vice president for national security and international policy at the Centre for American Progress.

"Trump likes the idea of undermining the European project, whether it's Brexit or anti-EU feelings," shared by Mr Trump and some leaders he has invited, said Ms Magsamen, a former national security aide to both presidents Barack Obama and George W Bush.

Mr Trump has met with the leaders of Britain, France and Germany overseas in 2019, but not at home. He will see close allies at the annual Group of Seven meeting this weekend in France, and is expected to soon invite new British prime minister Boris Johnson to the White House.

Like other presidents, Mr Trump takes advantage of overseas meetings such as the G7 and G20 to hold rounds of meetings that diplomats call speed-dating. Those meetings are typically shorter and less involved than a formal White House visit, which is usually the product of months of planning and internal jockeying for a spot on a president's crowded calendar, veterans of other administrations said.

The emphasis on Central and Eastern Europe echoes a similar effort at post-communist outreach under Mr Bush, but it comes in the different context of rising nationalism across the continent and cracks in the European Union. It also contrasts sharply with Mr Obama, who forged an especially tight bond with Ms Merkel during the global financial crisis a decade ago.

Mr Iohannis himself is not hostile to the EU, as Mr Trump is, and has criticised neighbour Hungary's swing towards anti-immigrant nationalism. But he is seeking Mr Trump's blessing as he goes to elections this fall and was eager to accept a coveted White House invitation.

Mr Trump wants to point to Romania as an example of Nato nations meeting their pledge to spend 2 per cent of gross domestic product on defence. Romania may also join Central European neighbours in opening or considering diplomatic missions in Jerusalem, a Trump administration priority after the United States broke decades of precedent to relocate the US Embassy in Israel from Tel Aviv to the holy city also claimed by Palestinians as a capital.

"This is an area that's very exciting; there's a lot going on there. Economies are growing. Trade between these countries and the US is increasing all the time," said the administration official, who spoke on the condition of anonymity under White House protocol.

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Daniel Fried, a former senior State Department official and ambassador to Poland, sees "mixed motives" in Mr Trump's focus on Central and Eastern Europe. Mr Fried, now a Europe specialist at the Atlantic Council, applauds the effort to draw these nations closer to the United States, even if "the ideological wing of the Trump White House likes them for the wrong reasons."

The Trump administration has especially sought out Poland, seeing it as a counterweight to German influence and priorities. Mr Trump has mused about relocating some US forces now stationed in Germany to a new headquarters in Poland, and will make his second visit as president to Poland over Labor Day weekend.

Western European diplomats shrugged off questions about whether their leaders feel slighted or at any disadvantage for the emphasis on generally poorer and less powerful nations.

Both British and American officials note that with the selection of Mr Johnson, a pro-Brexit conservative, Mr Trump now has a close ideological ally at the helm of one of the major Western allies.

French president Emmanuel Macron has stepped back from his role as the face of European efforts to talk Mr Trump out of punitive trade policies and confrontation with Iran. The two leaders were cordial, if a bit stiff, when they met on the side-lines of events commemorating the 75th anniversary of D-Day in June.

"We're doing a lot together, and the relationship between you and I and also the United States and France has been outstanding," Mr Trump said before he and Mr Macron met in the French city of Caen.

Ms Merkel has been pointedly critical of Mr Trump at times, including last month when she said his attacks on four Democratic lawmakers of colour run counter to what she considers "the strength of America."

"There have been opportunities for the two leaders to see each other outside of the White House this year," a German official said.

Ms Merkel has visited Mr Trump at the White House in both 2017 and 2018, but Mr Trump has not visited Germany as president. He is deeply unpopular in Germany.

Asked about Mr Trump's absence from Germany during the White House session on Monday, the administration official dismissed the notion of any slight to Ms Merkel.

"President Trump has frequent contacts with Chancellor Merkel, and this should not be read into any meaning for the US-German relationship," the official said.

Ms Merkel herself may have been studying up for her next meeting with Mr Trump, or perhaps just throwing a bit of shade with her reading selection on vacation this month.

Photographers captured Ms Merkel reading Harvard professor Stephen Greenblatt's Tyrant: Shakespeare on Politics, which former Bush administration State Department official Eliot A Cohen reviewed as "fundamentally a book about President Trump."