US vice presidents always yearn for a chance to share the spotlight, but when Kamala Harris got put in charge of the Mexico border mess, she might have been forgiven for secretly wishing she could return to the shadows.

Certainly the job is a high-profile opportunity to escape the notorious frustrations of being White House number two.

On Friday it was Harris -- not her boss, President Joe Biden -- who held a virtual meeting with Mexican President Andres Manuel Lopez Obrador.

"We thank President Biden for naming you to lead all things related to migration," Lopez Obrador said.

And in early June, it will be Harris making an official visit to Mexico and Guatemala, likely beating Biden's first trip abroad (to Europe) by about a week.

So what's the downside of running point on the southern border?

The southern border.

Few issues have as long a history of bedeviling both Democrats and Republicans as immigration and asylum on the approximately 2,000-mile (3,000-kilometer) US-Mexico frontier.

And what was already a tricky issue became outright toxic under Donald Trump, who built much of his presidency on demonizing undocumented immigrants and touting the need for a large wall.

So when illegal border crossings surged right from the start of his administration, Biden suddenly found himself in a perilous situation.

Harris, he decided, was the heavyweight figure to find an answer.

"When she speaks, she speaks for me," he said on March 24.

No border visits

Technically, Harris is not meant to deal with the border itself.

Her brief is to look for deeper solutions in the Central American countries where most of the migrants start from -- the "Northern Triangle" of El Salvador, Guatemala and Honduras.

Figuring out how to persuade those people to stay home was the main topic of discussion with Lopez Obrador on Friday.

But in reality, the public and certainly much of the Republican opposition don't draw the distinction.

One of the most frequent criticisms from Fox News and right-wing media outlets is that Harris has already failed by not visiting the border.

"The Northern Triangle," White House Press Secretary Jen Psaki said defensively in April, "is not the same as the border."

Yet to Harris' critics, the damage is done.

After all, she travels to many other places in the United States on vice presidential business. Why not to the sharp end of the crisis she wants to fix?

VP today, president tomorrow?

How this shakes out matters more because Harris came into the White House on January 20 with an unusual burden: at 78, Biden is the oldest president to take office and his deputy, 56, is seen by many as a leader in waiting.

Yes, Biden says he will seek a second term in four years, but he also does everything he can to boost Harris, who previously served as a senator and as California's attorney general.

"The president has given us clear instructions," Ron Klain, Biden's chief of staff, told The New York Times. "Our goal is to get her out there as much as we can."

Liz Peek, a contributor to Fox News, wrote in The Hill that the border role will doom Harris' ambitions.

"The odds of Kamala Harris ever being elected president are shrinking faster than a Creamsicle in August," she wrote. "It almost seems as though Biden's team was purposefully playing a dirty trick."

But Carl Tobias, a law professor at the University of Richmond, says Harris has "threaded the needle."

"Serving as VP has perennially been a difficult, delicate role because the vice president does not want to upstage the president," he said.

"Harris has seized this role as an opportunity to show that she can do excellent work on a thorny topic."