NEW YORK -- Donald Trump spoke of national unity to a son of Martin Luther King Jr., seeking to ease friction over the president-elect’s squabble with Rep. John Lewis, a protege of the slain civil rights leader.

But on Tuesday, a day after he sought to calm tensions, the president-elect went off on Twitter again about the Georgia Democrat.

John Lewis said about my inauguration, "It will be the first one that I've missed." WRONG (or lie)! He boycotted Bush 43 also because he... — Donald J. Trump (@realDonaldTrump) January 17, 2017

"thought it would be hypocritical to attend Bush's swearing-in....he doesn't believe Bush is the true elected president." Sound familiar! WP — Donald J. Trump (@realDonaldTrump) January 17, 2017

Trump met with King’s son on the holiday marking the life of the assassinated civil rights icon, just days after the president-elect had gone on Twitter to strike back fiercely at Lewis for questioning the legitimacy of the billionaire businessman’s election as president. Lewis and the elder King were among the Big Six civil rights leaders of the 1960s.

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In a post on his Twitter account, Trump had accused Lewis of being “all talk” after the Georgia Democrat said he didn’t think Trump had come to the presidency legitimately. Trump also tweeted that the Southern congressman should pay more attention to his “crime ridden” Atlanta-area district.

Trump’s comments drew widespread criticism, and have done little to reassure those uneasy about the transition from the Barack Obama, the nation’s first black president, to a president-in-waiting who struggled to connect with many nonwhite voters during the campaign.

The younger King downplayed the incident Monday, saying that “in the heat of emotion a lot of things get said on both sides.” King, who said he pressed Trump on the need for voting reform to increase participation, called their meeting “constructive.” King said that while he disagreed with the president-elect’s comments where Lewis is concerned, he believes “at some point in this nation, we’ve got to move forward.”

“I think we also have to consistently engage with pressure, public pressure,” King said. “It doesn’t happen automatically.”

Trump, who struggled for support from minority voters on Election Day, briefly joined King in the lobby of Trump Tower but ignored reporters’ shouted questions about his comments on Lewis, a civil rights legend in his own right.

The congressman said late last week he didn’t consider Trump a “legitimate president,” blaming Russian interference in the election. Lewis said he would boycott Friday’s inauguration. More than two dozen Democratic members of Congress have said they will sit out the Trump swearing-in ceremony. Among them is Tennessee Rep. Steve Cohen, who said Monday “this president ‘semi-elect’ does not deserve to be president of the United States. He has not exhibited the characteristics or the values that we hold dear.”

The Martin Luther King holiday is meant to honor community service and volunteerism, and many Americans, including President Barack Obama and first lady Michelle Obama spend part of the day undertaking a service project in their community. Trump, who canceled a planned trip to Washington, spent the day inside the Manhattan skyscraper that bears his name.

Also this week, Trump’s picks for Cabinet posts continue their trek to Capitol Hill to win support from lawmakers considering their confirmation for Cabinet positions.

On Tuesday, Republican Rep. Ryan Zinke of Montana was scheduled to make his case to be interior secretary. And Betsy Devos, Trump’s pick for education secretary, has a confirmation hearing Tuesday evening.

Trump’s tweets have stirred things up internationally, as well.

European Union nations bracing for Trump’s ascension showed defiance Monday in the face of the president-elect’s stinging comments on everything from NATO and German cars to the crumbling of the European Union.

German Foreign Minister Frank-Walter Steinmeier said the U.S. president-elect’s view that NATO was obsolete and his criticism that European allied members aren’t paying their fair share had “caused astonishment.”

Trump also said that Britain’s decision to leave the 28-nation EU would “end up being a great thing,” and he predicted that other countries would also leave.

At a meeting of EU ministers, French Foreign Minister Jean-Marc Ayrault said the best response to such comments was simple - “it is the unity of the Europeans.”

In Berlin, German Chancellor Angela Merkel insisted: “We Europeans have our fate in our own hands.”