WASHINGTON - Former President Barack Obama on Friday urged Democrats running for the White House not to lurch too far left in their pursuit of the nomination, while at the same time seeking to quell concerns in the party about its 2020 hopefuls and the messy primary season to come.

The comments - made in Washington at a meeting of the Democracy Alliance, a powerful network of liberal donors - marked some of Obama's most pointed words yet about a fluid primary in which he is not picking sides. They echoed previous comments in which he warned about the dangers of pursuing purity and rigidity in politics.

"This is still a country that is less revolutionary than it is interested in improvement," Obama said. "They like seeing things improved. But the average American doesn't think that we have to completely tear down the system and remake it. And I think it's important for us not to lose sight of that."

Obama did not name any candidates. But some Democrats associate the characteristics he described with Sens. Elizabeth Warren, D-Mass., and Bernie Sanders, I-Vt., staunch liberal candidates advocating sweeping change who are running near the top of the polls.

Beyond those two candidates, the contest has often been dominated by a discussion of ideas that were long seen as untenable, even in Democratic circles. Candidates have called for mandatory buybacks of certain firearms, decriminalizing border crossings and forgiving most or all student debt. In some cases, the proposals have come at a cost of tens of trillions of dollars, vast sums of money that would dwarf what Obama's administration spent and require historically steep tax increases on wealthy Americans. While some voters and activists have cheered this trend, President Donald Trump and his allies have been eager to highlight these themes.

However, Obama also warned the candidates against simply standing pat and campaigning on his accomplishments. Instead, he argued, they should try to "push past" them with new ideas. He pointed to his signature health-care law, which has been a focal point in the contest, as a prime example, calling it a "really good starter home."

Obama's vice president, Joe Biden, has campaigned aggressively on expanding the Affordable Care Act with an optional public insurance program, as has South Bend, Ind., Mayor Pete Buttigieg, another top candidate.

That has put them at odds with Warren and Sanders, who favor implementing a new Medicare-for-all system that would insure everyone through the government.

Obama did not indicate a preference Friday.

The former president seemed to be urging a balance between striving for bold new ideas and being in touch with voters' concerns. While it is the role of activists to push for dramatic change, Obama said, candidates should aim to win elections.

"My point is that even as we push the envelope and we are bold in our vision, we also have to be rooted in reality and the fact that voters, including Democratic voters and certainly persuadable independents or even moderate Republicans, are not driven by the same views that are reflected on certain, you know, left-leaning Twitter feeds or the activist wing of our party," he said.

The 44th president has been careful about commenting publicly about the contest. He has not spoken about it often, even as he has frequently met with and counseled the candidates in private over the past couple of years.

He said he has advised all of them to ask themselves the same basic questions: Why me? How will this impact my loved ones? And can I win?

The last question is one that has increasingly given Democratic donors anxiety as they assess the field. This week, it grew with the addition of former Massachusetts Gov. Deval Patrick, a staunch Obama ally who entered the race saying that neither the path trod by Biden nor Sanders and Warren "seizes the moment" in a way that insures a defeat for Trump. Meanwhile, former New York Mayor Mike Bloomberg also has taken steps toward running.

The 11th-hour moves reflect a primary unsettled by the fears of many Democrats worried that Trump will seize a second term. Obama urged them to not to be fretful.

"For those who get stressed about robust primaries, I just have to remind you that I had a very robust primary," he said, prompting laughter in the audience. He reminded those in attendance of his grueling 2008 battle with Hillary Clinton, which played out months before he won the presidency.

"We have a field of very accomplished, very serious and passionate and smart people who have a history of public service," Obama said. "And whoever emerges from the primary process, I will work my tail off to make sure they are the next president."

Even as he remains neutral in the primary, Obama is stepping deeper into the campaign. Next week, he will appear at a Democratic National Committee fundraiser in Silicon Valley.

The president spoke Friday in what was billed as a "fireside chat" with Stacey Abrams, the 2018 Democratic nominee for governor in Georgia and a rising star in the party. Obama praised Abrams and the work she is doing on voting rights with her recently launched organization.

As he concluded the roughly 45-minute discussion, Obama offered a final word of advice for the party's White House hopefuls.

"We have the better argument," Obama said. "We can't be arrogant about it. We can't take for granted that somehow people, just, you know, the scales will fall from their eyes at some point."