(CNN) Since leaving office in January, President Barack Obama has used written statements to defend the Affordable Care Act, denounce a decision to withdraw the US from the Paris climate accord, and, most recently, call for peace during Kenya's elections.

When he chose this week to respond to violent white nationalist protests in Charlottesville, Virginia, however, Obama used someone else's words instead of his own.

"'No one is born hating another person because of the color of his skin or his background or his religion...'" Obama wrote in the first of three tweets that quoted Nelson Mandela's autobiography , "Long Walk to Freedom."

"'People must learn to hate, and if they can learn to hate, they can be taught to love,'" read the subsequent dispatches. "'For love comes more naturally to the human heart than its opposite.'"

The first message became the most liked in Twitter's history, according to the social media company. It was sent on August 12, three days before President Donald Trump delivered a breathtaking defense of protesters, some of whom he said were 'very fine people,' marching among the neo-Nazis and white supremacists in Virginia.

Obama's tweet was paired with a photo of the former president smiling at a group of children in a window, taken near his youngest daughter's school in 2011.

The viral reach of Obama's message was a reminder of his popularity among Americans nostalgic for the type of reasoned emotion he often brought after national trauma.

But the measured response also reflected the balance all former presidents face when confronted with divisive or charged moments. Ex-presidents often keep their distance from such matters, especially during their successor's first year in office. Offering frequent public comments about a new president's actions can be seen as overly meddlesome and a hindrance to a new White House's ability to function.

"I cannot imagine just how upset both he and (first lady) Michelle Obama are. We know their character, we know their history," said Michael Nutter, the former Democratic mayor of Philadelphia.

"I am sure President Obama would like to say more," Nutter said. "He recognizes, though, where he is in these moments, and his proximity to having just been a president. So he's going to be careful. But those of us who do know him a little bit know where his head and heart is. He'll continue to express himself but it will continue to be in his terms and in his time."

A senior Obama adviser said this week that the former President was unlikely to weigh in directly on Trump's comments, which have drawn widespread condemnation from Republicans, corporate executives, and military leaders.

For Obama, who remains the object of frequent criticism from Trump and his allies in the right-wing media, speaking out overtly could also further galvanize the political base to which Trump is appealing.

As Trump offered a series of equivocal statements on the Charlottesville violence this week, it became clear that condemnation would be swift even from members of his own party, who have rebuked the President with varying degrees of severity.

Those critiquing Trump — at least implicitly — included the two most recent Republican presidents, who said the country must always clearly denounce the types of ideologies that Trump initially avoided criticizing.

"America must always reject racial bigotry, anti-Semitism, and hatred in all forms," wrote Presidents George H.W. Bush and George W. Bush in a statement Wednesday. "As we pray for Charlottesville, we are reminded of the fundamental truths recorded by that city's most prominent citizen in the Declaration of Independence: we are all created equal and endowed by our Creator with unalienable rights."

"We know these truths to be everlasting because we have seen the decency and greatness of our country," the Bushes wrote.

During his own presidency, Obama confronted racially charged matters in different ways. His comments usually sought to acknowledge the country's painful history with race while encouraging reconciliation.

His eulogy after the 2015 church shooting in Charleston , South Carolina, came amid another national debate over Confederate symbols. He said then that the Confederate flag that flew at South Carolina's state capitol was more than a historical remnant.

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"The flag has always represented more than just ancestral pride," he said. "For many, black and white, that flag was a reminder of systemic oppression and racial subjugation. We see that now."

Since January, however, Obama hasn't spoken publicly about race. Obama, along with first lady Michelle Obama, has spent the last several months appearing sporadically at a mix of paid and unpaid speeches. They've both been at work on book projects, and next week their oldest daughter begins college at Harvard.

This fall, he's due to campaign for the Democratic gubernatorial candidate in Virginia, though specific dates for his appearances haven't been set. The protests in Charlottesville, which left three people dead, are expected to upend the race.

Two days before he left office in January, Obama laid out the parameters for his post-presidential life.

"I want to be quiet a little bit and not hear myself talk so darn much. I want to spend precious time with my girls," he said during his final news conference at the White House, before adding that he would make his voice heard when political debates escalated beyond day-to-day matters.

"There's a difference between that normal functioning of politics and certain issues or certain moments where I think our core values may be at stake," he said.

Some of Obama's supporters say the current strife may rise to that level.

"Personally I always want to hear President Obama. We know that if this had taken place a year ago, the country would be in a very very different place," Nutter said. "I'm not asking President Obama to say anything. He can conduct his own affairs. But we know that it would be healing, it would bring this country together."