Photo: Eric Garcetti.

It's that time of year: celebrities, intellectuals and mayors offer guidance to grads.

Here in Houston, in addition to speaking at his alma mater, Houston Mayor Sylvester Turner was also honored with the University of Houston's President's Medallion for "heroism during Hurricane Harvey." Turner reflected on Harvey and other lessons in his speech, saying, "The road will not always be easy -- sometimes it will be highly challenging. But Cougar Pride don't turn back."

Across town, former New York City Mayor Michael Bloomberg told Rice University graduates to reject the "epidemic of dishonesty" he said characterizes too much of government. "Listen to people you disagree with without trying to censor them or shout over them,” he said. “And have the courage to say things that your own side does not want to hear," he said.

But graduation speeches aren't just about giving advice. For many politicians, these speeches can offer the opportunity to test the campaign waters far from home and practice lines for future stump speeches.

In New Hampshire, Los Angeles Mayor Eric Garcetti spoke to recent grads at South New Hampshire University, offering a pretty good look at what presidential candidate Garcetti might sound like: "To get here today, each one of you had to navigate borders — borders of geography, of opportunity, borders of identity and of your own doubt." He highlighted the country's increasing diversity and his place in it, describing himself as average: "I'm the average Mexican American Jewish Italian mayor of the most diverse city in the world." And he also took the chance to score some easy outsider points, criticizing the federal government in Washington, D.C.

"The pundits call it right now in our country that there are two Americas – there's the rural and urban divide, the immigrant and native-born, the coasts and the heartland, red and blue," he said. "I do believe there are two Americas, but it's none of those – it's Washington, D.C., and the rest of us."

And, for good measure, he offered this advice: "Don't forget to vote."

Also in New Hampshire for graduation season and another potential presidential candidate, former San Antonio Mayor and Secretary of Housing and Urban Development under Barack Obama, Julian Castro told graduates at New England College that they were the future. "You are exactly what our nation needs to prosper in this 21st Century," he said. "In this world where brain power is truly the new currency of success, you are our greatest hope to thrive in the years to come."

In an address that also touted diversity, former New Orleans Mayor Mitch Landrieu kept it simple; "do the most good for the most people in the shortest period of time," he told graduates at Saint Michael’s College in Vermont. "Don’t let anyone make you feel like you don’t deserve full participation in your community, in your civic life, in your church life and in our politics," he told the crowd.

Though mayors have experience running governments, they don't have the sort of name recognition other candidates often do, Jennifer Duffy, senior editor of the Cook Political Report, told Bloomberg News. Which is perhaps why, according to Bloomberg News, "no U.S. mayor has ever gone directly to the White House from City Hall." But that hasn't stopped a number of them from dipping their toes into the political waters ahead of the 2020 election. That experience might be enough, according to Peter Hart, an analyst and pollster who told Bloomberg News, “There’s every possibility a mayor will be seriously considered for president in 2020."