Democratic presidential hopefuls are struggling to find a succinct slogan that sums up any of their candidacies.

No one has crafted a bumper-sticker-sized message with the kind of appeal and simplicity of President Trump’s “Make America Great Again” tag line — which was borrowed from Ronald Reagan — a challenge for the candidates as they start to kick campaigns into high gear in the fall before key primary contests.

When asked after his campaign launch if he had a slogan like “Make America Great Again,” Biden gave a characteristically long-winded answer. "Make America moral again. Make America return to the essence of who we are, the dignity of the country, the dignity of people, treating our people with dignity," he said.

Late-night host Steven Colbert joked: “MAGA's over because Biden is coming at you with ‘MAMAMARTTEOWEATDOTCTDOTPTOPWD,’” he said, attempting to pronounce an acronym made from Biden's comment. “Little awkward to say, I admit, but it’s going to look fantastic on his hat.”

Biden later settled on "Our Best Days Still Lie Ahead," a sentiment expressed by President Barack Obama in 2011 and President Bill Clinton in 2000.

Vermont Sen. Bernie Sanders’s campaign promotes “Not Me. Us,” with “Feel the Bern,” a holdover tag line from his unsuccessful 2016 bid. The campaign of California Sen. Kamala Harris adopted “For the People” as its slogan, which it shares with the Morgan & Morgan personal injury law firm, which hosts its website on forthepeople.com. “For the People” was also the title of a now-canceled ABC courtroom drama series.

Massachusetts Sen. Elizabeth Warren hammers “We Persist” and “Dream Big, Fight Hard.” She also had some success with her campaign refrain "I have a plan," which has generated a range of "Warren Has a Plan for That" merchandise.

South Bend Mayor Pete Buttigieg, 37, often directly challenges Trump’s slogan and says there is “no honest politics that revolves around the word ‘again.’” His own campaign centers on generational change and promotes tag lines like “A new generation of American leadership” and “A fresh start for America.”

Tulsi Gabbard has promised to "Lead With Love" while Marianne Williamson urges Americans to "Join the evolution."

“None of them are very good or particularly inspiring,” veteran Republican political strategist Alex Castellanos told the Washington Examiner, adding that some candidates’ slogans seem unusually optimistic. “The future is not only promising, it is also perilous and scary these days. America may be in the mood for something more realistic than pure optimism. Something more like, ‘the future ain’t for wusses.’”

Hillary Clinton's presidential campaigns were dogged by struggles over which slogan to adopt. Leaked emails from August 2015 revealed 84 potential Clinton campaign slogans. ‘‘She tends to resist starting out with a message and working back to a program,’’ John Podesta, chairman of Clinton’s 2016 campaign, said early in her campaign.

Clinton’s campaign rolled out multiple slogans in 2016, including “Stronger Together,” “Forward Together,” “I’m With Her,” and “Fighting for Us.” In 2008 she tried out “Big Challenges, Real Solutions: Time to Pick a President," "Rebuilding the Road to the Middle Class," and, when Obama's "Change We Can Believe In" was catching fire: "Ready for Change! Ready to Lead!"

Part of the appeal of “Make America Great Again,” Castellanos said, is that it ties the comfort of the past to hope for the future. Trump’s campaign has sold over a million official red hats embroidered with iconic tag line. His reelection campaign altered the slogan to “Keep America Great,” but it still promotes “MAGA,” as well as “Promises Made. Promises Kept.”

Trump has insisted that he did not know about Reagan's use of "Let's Make America Great Again" in 1980 until after he had adopted the saying. Bill Clinton said in his 1992 presidential campaign announcement speech, in 1991, that "I believe that together we can make America great again."

Some Democratic candidate slogans don’t reveal much about their core messages, which could spell trouble for their campaigns. “You better know who you are and why you’re running. Voters aren’t going to tell you,” Castellanos said.

Biden's slogan, Castellanos noted, is at odds with Biden’s major appeal to voters: that he is a known, safe figure who represents a return to normalcy in the age of Trump. On the campaign trail, in addition to criticizing Trump, Biden paints himself as an optimist and says that America has great potential. But Biden’s tag line seems designed to “compensate for his weaknesses,” Castellanos said.

The former vice president faces primary opponents three to four decades his junior, and when voters hear 76-year-old Biden’s message that “Our Best Days Still Lie Ahead" it may elicit a skeptical response — 76.1 is the average life expectancy for an American male — “Well, not for you, Joe,” Castellanos quipped.

Some of the Democratic slogans are better than others, Castellanos said. Warren’s “We Persist,” and other messages encapsulate her liberal populist message, and New Jersey Sen. Cory Booker’s “We Rise” is one that “a campaign could work with” and “opens the door to emotion and drama.” Booker put his tag line to use in his speech at the New Hampshire Democratic Convention last weekend, prompting supporters to chant “we rise” along with him during his speech.