Barack Obama may have reached what he describes as “a major milestone on this journey” up the 2008 campaign trail. The senator from Illinois has now secured a majority of the “pledged” delegates to be chosen in the party’s primaries and caucuses.

Citing that achievement, Obama told wildly cheering supporters in Des Moines that he was now “within reach of the Democratic nomination for president of the United States of America.”

But Hillary Clinton is not going to let him grab the prize this week.

The lady is not quitting this contest just yet.

The pressure on Clinton to finish her run for the Democratic presidential nomination has been intense. And it will get more intense now that the results from Tuesday’s primaries in Kentucky (a loss for the Illinoisan) and Oregon (a win for the Illinoisan) have given Obama that pledged-delegate majority. The senator from New York’s keeping her campaign afloat by writing checks out of her own account. And she’s watching from the sidelines as Obama and Republican John McCain launch their fall campaigns against one another.

But there is one ironclad rule when it comes to races for presidential nominations: You don’t quit when you are winning primaries.

And Clinton has won another primary by a lopsided margin.

The former first lady took 65 percent of the vote in Kentucky to just 30 percent for Obama — almost as overwhelming win as she secured last week in West Virginia. That victory had her crowing Tuesday night that, “It’s not just the Kentucky bluegrass that music to my ears — it’s the sound of your overwhelming vote of confidence even in the face of tough odds.”

“You’ve never given up on me, because you know I’ve never given up on you,” told her cheering supporters in a speech that will be repeated as she moves her campaign on to Puerto Rico (where she should do well) and the last primary states of Montana and South Dakota (where Obama’s probably a little ahead).

Clinton’s had a good enough night.

There is little reason to believe, however, that she will get any more traction from the Kentucky win than she did from the West Viginia victory. Even as he lost Kentucky, Obama picked up enough delegates there to attain the bragging rights that go with the pledged-delegate majority. And his solid win in Oregon padded the margin.

Every indication is that the unpledged super-delegates who have it in their power to “seal the deal” for the eventual nominee will continue to break his way.

“The Democratic Party through the democratic process has spoken,” Connecticut Senator Chris Dodd, a former presidential candidate who has endorsed Obama. “The super-delegates aren’t going to change that.”

Dodd predicted that party leaders will ultimately allow delegations selected in the disputed January primaries in Michigan and Florida will be seated at the convention in August, but not with a big advantage for Clinton. “I think it will be an even split,” said Dodd, who added that he believes the race is essentially “over.”

But Clinton will soldier on. She’ll point to the fact that she did very, very well in Kentucky — running up a 250,000 margin in the popular vote, and winning women and men, rich and poor, college graduates and high-school drop outs, liberals and conservatives, Protestants and Catholics, suburbanites and rural folks and just about every other group except the state’s small African-American population. She’ll suggest, again, that she can win blue-collar voters and Obama cannot. And she’ll continue to peddle the line that a lot of Democrats will cross over to back Republican McCain in November if she is not the party’s nominee — pointing to the Kentucky exit polls that suggest that, in an Obama-McCain race, 32 percent of Democratic primary voters who back McCain while 15 percent would not vote.

Clinton’s not a bitter ender.

When Obama gets the majority of delegate commitments — from pledged delegates and super-delegates — she will quit the race. But until she really has been defeated, Clinton will keep running.

Nights like this guarantee that.

UPDATE: Video from Obama’s victory speech in Iowa below.