Sen. Clinton, D-N.Y., gains the support of Sen. Obama, D-Ill., the man who beat her in the most closely contested and bitter Democratic primary in decades, and of a grateful Democratic Party establishment to pay off the $10 million debt she ran up during her unsuccessful presidential campaign.

Clinton will also retain and enhance her leadership role among Democrats in the Senate, a forum she has come to love and in which she has proven herself extremely able.

And her support on the campaign trail ensures Obama what he most needs: a strong, united Democratic base as he heads into the summer and fall campaigning season against Republican presidential standard-bearer Sen. John McCain of Arizona.

Clinton proved herself an energetic and effective campaigner in her losing battle with Obama, especially with key core Democratic constituencies he must win to assure the presidency in November's election.

There was always much more wishful fantasy than fact in GOP claims that women were deserting Obama in significant numbers to back McCain instead. Recent polls consistently have shown a clear preference from female voters for Obama over McCain. But Clinton's new no-holds-barred commitment removes any doubts of that and should give Obama a boost he needs among middle-aged and older Hispanic voters, and among blue-collar, working-class male Democrats, who proved to be among Clinton's most loyal supporters in her race.

Obama may yet reward Clinton for her support with the vice presidential spot on his ticket. Even if he doesn't, she may have the option of a high-profile position in his administration if she wants it. Or she may elect to stay in the Senate: That would be another win-win proposition for her.

If Clinton stays in the Senate, she could play a leading role in crafting a raft of legislation on issues from Social Security reform to welfare in the next 111th Congress. If Obama wins the November election, he may well enjoy 60 percent-plus majorities in both the U.S. Senate and the House of Representatives. That would give Clinton, as one of the most high-profile and powerful senators on Capitol Hill, enormous clout in forming bills that could shape the United States for decades to come.

And if Obama wins but then fails to master the mountain of problems, from Iraq to the collapsing dollar and the soaring gasoline crisis, then Clinton will be perfectly positioned to either run against him or to seek the presidential nomination again in 2012 if Obama stands down. For she has now nailed down the crucial questions about her loyalty to the Democratic Party over her personal ambition.

The Democrats therefore face the fall campaigning season much more united than the Republicans. Hard-core conservatives still distrust McCain, and many have been adamant that they will stay at home and not vote for him. McCain continues to trend well ahead of his struggling congressional party in polls, but he will lack the traditional GOP advantage that Republicans fight presidential campaigns far more united and disciplined than the traditionally fractious Democrats do.

Obama has repeatedly shown political genius in his presidential campaign since sweeping the Iowa caucuses in January. In making his peace with Clinton and enlisting her to his side, he has done so yet again.