This month, President Obama offered the Southwest light-rail line $125 million.

Last week, 8-year-old Karlis Barobs offered $75. Plus a lot of love.

The Hopkins boy, a “trainiac” since before he could walk, hopes to see the Southwest line come to his hometown. So he wants to give it a share of the $300 his classmates at the Minneapolis Latvian School raised for him after they learned he has cancer.

Karlis has decided that one-fourth of his classmates’ gift will go to UNICEF, one-fourth to Pennies for Patients (a group that fights leukemia and lymphoma with small donations) and one-fourth to his family.

He wants the rest — $75 — to go to the $1.79 billion rail line.

“If we can pay a little of that, we can help them build it,” Karlis said in a recent interview conducted — where else? — on the Blue Line train between downtown Minneapolis and the airport.

Karlis has taken trains coast to coast, from cable cars in San Francisco to Amtrak’s Acela Express in the Northeast. He’s ridden the high-speed Renfe train in Spain. When the Green Line opened in 2014, Karlis and his parents stood in the rain to get a ride on opening day.

Late last year, Karlis developed a swollen lymph node. At first, his parents thought it might be strep throat. But when the lump kept growing, they took him to the doctor. The diagnosis: Burkitt’s lymphoma.

His prognosis is good. Burkitt’s is considered a treatable form of cancer, and Karlis’ was discovered early. Regular chemotherapy at Minneapolis Children’s Hospital has cost him about half his blond hair, but it hasn’t fazed him, according to his mom, Jane Meyer.

“When this began, he said, ‘Mama, am I going to lose my hair?’ ” she recalled. “I said, ‘Probably, yes.’ And he said, ‘All right! No more haircuts!’ ”

Karlis recently learned that the future of the Southwest line, at the center of a bitter political struggle in recent years, was in doubt. Karlis saw a YouTube video in which Choo Choo Bob, star of the locally produced children’s TV show, explained that Southwest was going to cost much more than originally planned.

“I thought, ‘Oh, my gosh, what happened here?’ ” Karlis said. “I want to see a train station in Hopkins.”

That’s when he got the idea to donate some of his cancer money to the train — a plan that, it turns out, may not be as easy as you’d think. Adam Duininck said he’s pretty sure that the Metropolitan Council couldn’t accept such a donation directly.

‘A very sweet gesture’

“It’s a very sweet gesture,” said Duininck, who chairs the Met Council. “And it’s wonderful to hear of his passion for trains and for this project. I am really flattered that he takes an interest in public transit and public policy.”

There are other ways Karlis could support the line, Duininck said. For example, he could donate the money to a community fund set up by several west metro suburbs to fund things like station art and landscaping that were cut from the project to save money.

Duininck said he would get in touch with Karlis’ family and invite the youngster to tour the light-rail maintenance and operations center, and perhaps even take a train ride in the operator’s cab.

Karlis’ interest in transportation now includes planes. At home, he’s turned an air hockey table into a giant train station and airport complex, and he’s starting to think about a career as an aircraft designer.

But you never forget your first love.

“Trains are cool,” Karlis said. “They have a great history, and they have cool names. It’s gonna be awesome to have a light rail in Hopkins.”