Domestically, Mrs. Clinton has tackled complex policy issues, sometimes failing. She has shown a willingness to learn and change. Her current proposals on health insurance reflect a clear shift from her first, famously disastrous foray into the issue. She has learned that powerful interests cannot simply be left out of the meetings. She understands that all Americans must be covered  but must be allowed to choose their coverage, including keeping their current plans. Mr. Obama may also be capable of tackling such issues, but we have not yet seen it. Voters have to judge candidates not just on the promise they hold, but also on the here and now.

The sense of possibility, of a generational shift, rouses Mr. Obama’s audiences and not just through rhetorical flourishes. He shows voters that he understands how much they hunger for a break with the Bush years, for leadership and vision and true bipartisanship. We hunger for that, too. But we need more specifics to go with his amorphous promise of a new governing majority, a clearer sense of how he would govern.

The potential upside of a great Obama presidency is enticing, but this country faces huge problems, and will no doubt be facing more that we can’t foresee. The next president needs to start immediately on challenges that will require concrete solutions, resolve, and the ability to make government work. Mrs. Clinton is more qualified, right now, to be president.

We opposed President Bush’s decision to invade Iraq and we disagree with Mrs. Clinton’s vote for the resolution on the use of force. That’s not the issue now; it is how the war will be ended. Mrs. Clinton seems not only more aware than Mr. Obama of the consequences of withdrawal, but is already thinking through the diplomatic and military steps that will be required to contain Iraq’s chaos after American troops leave.

On domestic policy, both candidates would turn the government onto roughly the same course  shifting resources to help low-income and middle-class Americans, and broadening health coverage dramatically. Mrs. Clinton also has good ideas about fixing the dysfunction in Mr. Bush’s No Child Left Behind education program.

Mr. Obama talks more about the damage Mr. Bush has done to civil liberties, the rule of law and the balance of powers. Mrs. Clinton is equally dedicated to those issues, and more prepared for the Herculean task of figuring out exactly where, how and how often the government’s powers have been misused  and what must now be done to set things right.

As strongly as we back her candidacy, we urge Mrs. Clinton to take the lead in changing the tone of the campaign. It is not good for the country, the Democratic Party or for Mrs. Clinton, who is often tagged as divisive, in part because of bitter feeling about her husband’s administration and the so-called permanent campaign. (Indeed, Bill Clinton’s overheated comments are feeding those resentments, and could do long-term damage to her candidacy if he continues this way.)