In this undated photo released by the White House, the Obama family’s new dog, Bo, a 6-month-old Portuguese water dog, is shown at the White House in Washington.

Washington ? Let’s follow the trail.

The Obama puppy trail.

Why? Because it is our duty.

It starts at a doggie love shack on the bank of a creek in far western Pennsylvania and ends at 1600 Pennsylvania Ave. Along the way, the world’s suddenly most famous puppy has had ups and downs. He has known rejection and the joy of newfound affection.

The White House tried hard, oh so hard, to keep 6-month-old Bo a secret. But the Obama girls’ new pet, that cuter-than-cute Portuguese water dog with the lei around his neck, is a celeb now. And this is his story.

One day last August, a pretty Portie named Penny was led into the boudoir — also known as the grooming room — at Julie Parker’s kennel in Millcreek Township, outside Erie, Pa.

Watson, a studly Portie with a history of siring champion dogs, took to her immediately.

“There was a little kissy kissy, huggy huggy, licking of the ears,” Parker recalled in an interview Sunday.

While Parker sipped a Budweiser and held Penny’s leash, Watson did what stud dogs do. Was it love? Apparently not.

“I don’t think Watson cares,” said Parker, who hadn’t heard that her dog sired the First Puppy until we called her Sunday.

After her one-night stand, Penny went home to Texas, where she lives with Art and Martha Stern on a 10-acre ranchette in the town of Boyd, outside Dallas. The Sterns are big dogs in the Portie world because they are the breeders of the previously most famous Porties in the universe, Sen. Ted Kennedy’s.

Until a few years ago, the Sterns lived in Fairfax County, Va., and Martha worked in facilities management at the Justice Department in Washington. But puppy love sent them, in retirement, to more wide-open spaces.

Penny’s blessed event took place at the Stern place Oct. 9: Ten — count ’em, 10! — puppies in one litter. The Sterns, whose operation is called Amigo Portuguese Water Dogs, give theme names to each of their litters, and being fans of then-candidate Barack Obama, they dubbed this one the Hope and Change Litter.

Soon, Martha Stern says, Kennedy was sniffing around for another pup. He had his eye on a curly-haired one named Amigo’s New Hope, she said. But she talked him out of it because she thought a “less pushy” wavy-haired dog would be a better fit for the Kennedy family because they already had two older Porties.

They didn’t know it at the time, but Amigo’s New Hope — which almost became a Kennedy dog — was on its way the White House, but not without some twists and turns.

So, another puppy from the litter — eventually named Cappy — went to the Kennedys, said Martha Stern, who was particularly empathetic to Kennedy’s battle with brain cancer because she is in chemotherapy for lung cancer. Porties typically sell for as much as $2,000 apiece, and the others went fast: one to Alexandria, Va., one to Dallas, several to Austin and several more to Houston.

Like all the Sterns’ pups, Amigo’s New Hope underwent a “temperament test,” Art Stern said. They tested whether he would freak out when an umbrella was opened in front of him or when there was a loud noise. Amigo’s New Hope did well, Art Stern said — not too shy, not too aggressive.

Eventually he was placed with a woman in Washington, Stern said. She renamed him Charlie. Alas, it wasn’t to be a happy home.

The woman — who has not been identified — has an older Portie, Martha Stern said, and that playful little scamp Charlie was getting on the other dog’s nerves. Charlie thought the older dog might be his mommy, and even attempted to nurse, Stern said. Finally, early in March, the woman decided enough was enough.

Charlie needed to find a new home.

Portie breeders tend to be a careful lot, and they insist on finding new homes for unwanted pups to assure they don’t end up in shelters. Rejected by his first family, Charlie was about to set on a journey that took him to the first family.

Kennedy’s wife, Victoria, suggested he would be perfect for the Obama girls, the Sterns said. Arrangements were made for Charlie to be tutored in good manners by Dawn Sylvia of Merit Puppy Training , in Hume, Va.

This began the Super Secret phase of Charlie’s life, which included a clandestine White House visit in which he won over the Obama girls and their parents. Then Easter weekend came, and his days of anonymity ended. The celebrity Web site TMZ.com, and The Washington Post published online pieces identifying the new White House puppy as a Portie. The Post disclosed that Sasha and Malia had renamed him Bo.

Washington is waiting for the first official, live-action glimpse of the Obama’s new puppy. The black-and-white cutie who began life as Amigo’s New Hope, then became Charlie, then became Bo is slated to make his White House debut Tuesday, though some still are speculating he might show up today at the Easter Egg Roll.