Her experience. His charm and fundraising ability. His support among liberals, independents and black voters. Her hold on white female voters, low-income Democrats, and Latinos.
With energized Democrats facing a difficult choice between two historic, formidable candidates vying to be the nation's first black or first women president, some have suggested that the two join forces on a single Democratic "dream ticket."
Dream Ticket or Democratic Fantasy?
Fresh from her victories in Ohio, Texas and Rhode Island, Sen. Hillary Clinton, D-N.Y., appeared on network morning news programs Wednesday and suggested that a joint ticket with Sen. Barack Obama, D-Ill., is a real possibility.
On CBS' morning program, anchor Harry Smith said to Clinton, "We talked to a lot of people in Ohio who said there really isn't that significant a difference between you two, and they'd like to see you both on the ticket."
"Well, you know, that may be where this is headed." Clinton said. "But of course we have to decide who is on the top of the ticket. I think the people of Ohio very clearly said that it should be me."
On a plane from Texas to Chicago Wednesday, Obama smiled wryly when asked about the possibility of a joint Clinton-Obama or Obama-Clinton ticket.
"You know, we are just focused on winning this nomination," he said. "That's my focus. And you know, I've said before I respect Sen. Clinton as a public servant. She's a tenacious opponent. I think it is very premature to start talking about a joint ticket … right now."
Obama minimized the importance of Clinton's victories. "We had won 12 in a row. She won two," Obama told ABC's Diane Sawyer Wednesday morning on ABC's "Good Morning America" -- not counting Clinton's third March 4 win in Texas.
"These were states that she had huge leads going into it, and we closed that gap, but we couldn't close it as much as we'd like," Obama told "GMA." "It's going to be very hard for her to catch up on the pledged-delegate count."
For her part, Clinton continued to hammer away at Obama's national security credentials, suggesting she's the best one who can take on Sen. John McCain, R-Ariz.
"This election now is not only between Sen. Obama and myself. It is, in the voter's mind, between one of us and Sen. McCain. I think that's why I did so well last night," Clinton said Wednesday on "GMA."
"I think national security is the issue against John McCain. I think it is not only legitimate, it's necessary to ask voters to determine who they would like to see as commander in chief," Clinton added. "Now it's a real choice, because we know who the Republican nominee is going to be, and I think voters are going to want someone who can stand up on that stage, toe-to-toe with John McCain."
Joint Ticket Talk -- Good Tactic?
Some Democratic strategists say Clinton's suggestion that she is open to a joint ticket is smart strategy.
With only a handful of primary contests left, the possibility of a joint ticket could win her some Obama supporters who have reservations about his candidacy.
Conversely, a joint ticket could reassure those who believe Obama has a better shot against Republican nominee McCain in the general election.
"It's a way for her to play at 'If you like Obama and you're a little bit worried about his experience, don't worry, you can vote for me and I'll pick him,'" said Joe Trippi, who was the chief adviser to former Sen. John Edwards in his 2008 bid.
"It doesn't mean she'll actually pick Obama," said Trippi, who now works as a CBS contributor.
Trippi said Sen. John Kerry's campaign did the same thing in 2004 with Edwards, putting out the word in Iowa and other states that it was considering Edwards for vice president.
"People just said, 'Great. I can vote for John Kerry and I get John Edwards, too,'" Trippi said. In the end, Kerry did choose Edwards as his running mate for their failed 2004 bid against President Bush.
"Clinton's comment is designed to give permission to Obama supporters to go ahead and support Clinton," agreed Democratic pollster Margie Omero, who isn't affiliated with either campaign.
Other Democratic strategists argue that the "dream ticket" is really more of a fantasy, given the intense and sometimes bitter nomination battle.
"This is tactical silliness," said Democratic strategist Anita Dunn, who has worked with Obama in the past. "This is going to be a tough campaign that's going to go on for at least several more weeks."
Historically, bitter primary opponents have sometimes put aside their animosity to join forces for the general election.
John F. Kennedy made peace with his primary opponent and eventual vice president Lyndon B. Johnson. George H.W. Bush assailed Reaganomics as "voodoo economics," then came onboard as Reagan's vice presidential pick.
Dunn also said Clinton's remark about being at the top of the ticket denotes some chutzpah.
"It's highly unusual for the person in second place to be talking about putting the other person on their ticket as vice president," she said.
On a conference call with reporters Wednesday, Clinton's chief strategist Mark Penn demurred when asked whether Clinton would be open to being Obama's vice presidential pick.
"I'm not going to interpret her remarks beyond what they are," Penn said. "We are super focused on winning the nomination, and we're not really commenting or going beyond that."
The "dream ticket" scenario was also floated before the multistate Super Tuesday votes in February. "Would you consider an Obama-Clinton or Clinton-Obama ticket going down the road?" asked CNN's Wolf Blitzer during a CNN debate in January.
"Well, there's a difference between those two," Obama laughed. "But her service to this country has been extraordinary. And I'm glad that we've been walking on this road together."
"Well, I have to agree with everything Barack just said," Clinton said.
A March ABC News/Washington Post poll found 36 percent of Democratic voters polled said that if Obama wins, he should choose Clinton as his running mate; 11 percent preferred Edwards and 3 percent preferred New Mexico Gov. Bill Richardson. Former Vice President Al Gore and Delaware Sen. Joe Biden each got 1 percent.
Women were much more likely than men to say Obama should choose Clinton, 41 percent to 28 percent. During the 2008 campaign, Edwards, the 2004 Democratic vice presidential pick, maintained that he was running for president, not vice president. But Edwards' supporters argue he would be a great pick.
"He has said no, but I would certainly hope that he would serve, if asked, as vice president or attorney general," Trippi said. "There are a lot of us who hope he will get asked and that he will serve."
With McCain securing the Republican nomination Tuesday night, and Clinton and Obama entrenched in a fight that could go all the way to August's Democratic Party convention in Denver, Republicans hope that a drawn-out battle will be a disadvantage for Democrats going into the general election.
Trippi said even if the nomination is settled on the convention floor, the Democrats will mount a vigorous general election campaign.
"Look at the energy, the money, the massive turnout. These are two candidates that Democrats are very excited about," Trippi said.
"Either one of them on their worst days raised more money than McCain's been able to raise, and has more excitement and energy and have turned out more voters than McCain's turned out," he said. "I'd be really worried if I were on the Republican side right now."
ABC News' David Wright, Sunlen Miller, Jake Tapper and Avery Miller contributed reporting.