John F. Kerry has shattered fundraising records, unified an oft-warring party and pushed past President Bush in some national polls. Yet many Democratic voters, officials and even members of Kerry's staff express an ambivalence -- or angst -- about their presidential candidate that belies this strong public standing.

These Democrats say the enthusiasm for defeating Bush runs much stronger and deeper than the passion for electing Kerry. The chief reason: The senator from Massachusetts, they say, has not crisply articulated what a Kerry presidency would stand for beyond undoing much of the Bush agenda.

So far, these concerns have not slowed Kerry. But if Kerry cannot change this perception coming out of next month's Democratic convention in Boston, it could prove much harder for the party to maximize turnout, win over Ralph Nader voters and keep independents from swinging to Bush, they say.

"There is a danger in that [ambivalence]," said John D. Podesta, White House chief of staff in the Clinton administration. "You can't just be against something. [Voters] want a positive vision of where the country is going, and he has to provide that."

Rep. Bart Gordon (D-Tenn.) said for Kerry to win the presidency, "Bush has to lose the confidence of the public and the next thing that has to happen . . . [is] Kerry has to convince the public he's an acceptable alternative. He has not passed that threshold, but he is making progress."

Asked whether he is excited about Kerry's candidacy, Gordon said, "I am excited about a change of the administration. I think Kerry is a solid guy; he's not an exciting guy."

To be sure, Kerry heads into the summer stretch in far better shape than many Democrats -- and Republicans -- anticipated only months ago, and is far better positioned than most challengers in recent history.

He raised more money in April and May than Bush, the most prolific fundraiser in presidential history; silenced most of his critics inside the party; and jumped ahead of the president in polls, both nationally and in several key battleground states. Rep. Rahm Emanuel (D-Ill.) said this proves most Democrats are fired up about Kerry.

As for those who are not, "there were days when people had lukewarm feelings toward Bill Clinton, and now he's revered," he said. "Do you think they will do any less to help John Kerry?"

One standard barometer of voter enthusiasm is how strongly partisans support their presidential candidate. By this measure, Kerry is doing far worse than Bush, but markedly better than Al Gore at this point in 2000. In a recent Washington Post-ABC News poll, 68 percent of Democrats strongly supported Kerry and 89 percent of Republicans expressed strong support for Bush. In July of 2000, 55 percent of Democrats expressed similarly strong feelings toward Gore.

It is not uncommon for first-time presidential candidates to face questions at this point in the campaign about their ability to inspire and connect with voters. Tad Devine, a senior Kerry adviser, said that John F. Kennedy did not really catch on with voters until his debates with Richard M. Nixon late in the 1960 campaign. Devine said most successful candidates made their move -- and mark -- during or after their convention, when most voters tune into the presidential campaign and the nominee has synthesized his message.

Taking a cue from Ronald Reagan, Clinton and Bush, all of whom succeeded in explaining to voters three or four easy-to-understand changes they had in store for the nation, Michael Donilon and other top Kerry advisers are crystallizing the Democratic nominee's core initiatives for unveiling at the convention.

Devine said the campaign is developing a positive message around the concept of "making America stronger at home and respected in the world. The challenge is to infuse meaning into this" in the months ahead with specifics.

Devine said there will be at least three opportune moments to do this: when Kerry names his running mate, which a top aide said will happen the first or second week in July; at the convention a few weeks later; and during debates with Bush this fall. For now, Kerry is content raising money to wage a forceful campaign and spending millions of dollars on ads introducing himself as a candidate with the stature to run the country during wartime. Polls show Kerry's image has improved in many states in which his campaign spent heavily on biographical ads.

Yet many Democrats are concerned that Kerry will have a harder time than previous candidates detailing his positions in a way voters can readily understand. Kerry holds nuanced positions on many issues, such as trade, that do not translate into 30-second sound bites. One of his plans -- cutting taxes for corporations in exchange for ending overseas tax-dodging -- is not easily explained and turns off many liberal Democrats because it includes tax breaks for wealthy corporations.

Despite spending 20 years in the Senate, Kerry has not left a distinct policy mark, having chosen to focus more on investigations. And, at times, he has straddled both sides of issues. The Bush campaign frequently chides Kerry for voting for Bush's plan for education and the Patriot Act, only to criticize both on the campaign trail. In the middle of June, "it's unclear what John Kerry's vision and message [are] for the country," said Steve Schmidt, spokesman for the Bush campaign.

Even on abortion rights, which Kerry has consistently supported, his staff is unclear about whether he would appoint lower-court judges who oppose Roe v. Wade.

A top Democratic aide, who requested anonymity to speak candidly about Kerry, said many House members and staff say it is hard to explain what Kerry stands for, and what he has stood for in the past. The aides said the Kerry campaign is aware of this concern and committed to addressing it.

At this point in 2000, it was clear Bush stood for lower taxes, sweeping education changes and a strong military. In 1992, it was clear Clinton was a "new kind of Democrat," who would cut taxes for the middle class and revamp health care.

Kerry adopted a cautious approach to this campaign, anticipating that factors outside his control, such as Iraq and terrorism, could alter the race at any moment, a top aide said. A senior Kerry adviser, who requested anonymity, said this has left many on the staff wanting, both in terms of strong leadership and inspiration.

Kerry may never stir Democrats passionately, but he may not need to. Since his earliest days in politics, Kerry has appeared somewhat detached from the people and voters who helped elect him. He is cerebral, and his interests -- such as windsurfing -- and his wealth separate him from the general public. Despite Kerry's two decades in the Senate, not many Democrats consider themselves "Kerry Democrats" or ardent loyalists, or even close friends.

But few doubt his seriousness and stature, which many Democrats think voters are looking for in this election. The danger is if voters come to see Kerry as a candidate more of ambition than ideas and more calculating than complicated, Democrats say.

Although Democratic constituencies from unions to abortion rights activists remain committed to Kerry despite concerns about his commitment to their issues, the durability of that loyalty could be tested soon.

Many Democrats are bracing for a Bush resurgence -- if not in the weeks ahead, then after the GOP's national convention in August. After Bush's poll numbers dropped to what history says are perilous levels, he has hit a run of potentially good fortune.

Bush's plan to return power to the Iraqis at month's end is gaining support after the United Nations unanimously voted in favor of the U.S.-sponsored resolution. Back home, the economy is humming again. Nearly 250,000 jobs were added in May, oil prices are dropping and there are signs of a sustained turnaround even in the hardest-hit manufacturing belt.

"We are seeing some upturns," said Wisconsin Gov. James Doyle (D). Wisconsin, which has the second-highest percentage of manufacturing jobs in the nation, has been trimming unemployment rolls at a steady clip in 2004. "I am pretty confident . . . we are turning around. I think it helps [Bush] some."

All of this sets up the Democratic convention in Kerry's home town of Boston in six weeks as a potentially make-or-break moment for the nominee.

"He has a problem in that people don't know him and don't have a great affinity for him," said former representative Tony Coelho (D-Calif.), who chaired Gore's campaign. "The time is coming when he has got to get people turned on. Right now, you just got to be in the game, and he's there."

Polling director Richard Morin contributed to this report.

Regarding Sen. John F. Kerry's image, an ex-Clinton staffer said voters "want a positive vision of where the country is going, and he has to provide that."