In securing the Democratic presidential nomination, Barack Obama has scored an electrifying breakthrough that transforms the face of American politics. He has not yet won the White House — but he has a good shot. And he certainly has won the right to be free of Hillary Clinton.

Someone should send the New Yorker a memo: “Hello, you lost.’’

Her graceless speech Tuesday night demonstrates why Obama would be foolish to have her as his runningmate. With her husband, former President Bill Clinton, clearly urging her on, Senator Clinton is trying to muscle her way into the vice presidency.

On Tuesday night, she acknowledged Obama’s accomplishments but did not concede. She continued to portray herself as the person who’d be the Democrats’ strongest standardbearer, and she said she wanted the nearly 18 million people who voted for her to be “respected.’’ She urged supporters to go online and share their thoughts about what she should do now.

They adore her, and I’m not holding my breath waiting for them to beg her to pack it in or to rule out any idea of being VP.

Obama can’t afford to look weak, to be bullied by her or her husband, who is unable to cede the limelight and whose ham-handed comments over the months about Obama angered blacks and whose episodic tantrums are embarrassing.

Putting Senator Clinton on the ticket would cause a more fundamental problem for Obama. It would undercut his message of change — change from Washington insiders, bitter squabbling, and a pattern of Bush-Clinton-Bush.

Her threshold 2008 problem was her 2002 vote to authorize the Iraq war — and her refusal to apologize for it. Obama, opposed to the war from the start, exploited her flaws in this regard and raised serious doubts about her judgment. And now what — he’s supposed to say, “Oh well, forget about all that’’?

Another Clinton mistake was calling herself the voice of experience and projecting her nomination as inevitable. Voters hungering for change were turned off by her experience. No Democrat is entitled to the presidential nod.

Nor is one entitled to be VP; yet that’s precisely the signal Clinton is sending.

Obama also needs to think: “Down the line, in office, do I really want to have her at my side second-guessing me all the time, and him third-guessing me?’’

Meanwhile, it was fascinating to watch on TV as Obama celebrated on Tuesday night, in the same St. Paul arena in which Republican Sen. John McCain will be nominated.

No matter whether you intend to vote for Obama in November, and no matter what role race may yet play in the election, you had to marvel, at least for an instant, that a black person in 2008 had emerged as his party’s choice for president.

Still more breathtaking will it be if, should Obama win, he can achieve the vision he sketched:

“Generations from now, we will be able to look back and tell our children that this was the moment when we began to provide care for the sick and good jobs to the jobless; this was the moment when the rise of the oceans began to slow and our planet began to heal; this was the moment when we ended a war and secured our nation and restored our image as the last, best hope on Earth. This was the moment — this was the time — when we came together to remake this great nation so that it may always reflect our very best selves, and our highest ideals.’’

That would really be something.

M. Charles Bakst is The Journal’s political columnist.

mbakst@projo.com /(401) 277-7638