Obama and Clinton take their battle to Ohio and Texas, states Clinton admitted this week, will be crucial for her candidacy.
With neither candidate poised to reach the 2,025 delegates needed to win the nomination before the party's August convention in Denver, the Democratic battle has become a state-by-state fight for delegates and momentum.
Obama now holds a 94-delegate lead over Clinton, according to ABC News' delegate scorecard.
Since Obama swept the Potomac primaries last week in Virginia, Maryland and Washington, D.C., Clinton has sharpened her attacks, suggesting her opponent is all talk and no action.
Asked about a speech Obama gave last weekend in Wisconsin, in which he borrowed lines from Gov. Deval Patrick, D-Mass., Clinton didn't comment directly on the plagiarism assertion, but did suggest Obama's candidacy is about rhetoric, and little else.
"The real issue is, if your entire candidacy is about words, they should be your own words," Clinton said during a satellite interview with KGMB, the CBS affilliate in Honolulu.
"And you may know that both Deval Patrick and Sen. Obama have the same consultant and adviser, who is apparently putting words in both of their mouths," she said.
Obama argued Clinton has used lines from his speeches, too. Patrick, who has endorsed Obama, has defended his friend.
Accusations of plagiarism aren't the only themes dominating the discussion, as voters in Wisconsin and Hawaii headed to the polls.
The subject changed from plagiarism to party politics after an unnamed Clinton official told Politico that both campaigns would go after the pledged delegates if there is a stalemate between the candidates, going into this summer's Democratic convention.
On separate conference calls with reporters, both campaigns denied they plan to poach each other's pledged delegates.
The Obama campaign linked the story with the Clinton campaign's attempt to get Florida and Michigan delegates seated at the convention.
Clinton won in both states where the Democratic Party had stripped them of their delegates, as punishment for moving up their primary dates.
"The Clinton campaign has once again floated a strategy that would essentially say that the preference of Democratic voters is a mere obstacle to their win-at-all-costs strategy," Obama campaign manager David Plouffe said in an e-mail to reporters, Tuesday.
Focusing on the economy, Obama campaigned in Texas, Tuesday, while Clinton focused on Ohio, where she currently holds a strong lead in the polls.
Targeting working-class voters, Clinton launched a new ad campaign in Ohio, called "Night Shift," suggesting the New York senator can relate to the underpaid, overworked person, pouring coffee or working the night shift at the local hospital because she's worked the night shift, too.
Beginning Wednesday, Emily's List, a group that works to elect female candidates who support abortion rights, and has endorsed Clinton, will send mail and call non-college-educated women, rural women and older women squeezed by economic pressures. Using a peer-to-peer tactic, the group will use Ohio women to contact these women and urge them to vote for Clinton.
Both Obama and Clinton have adopted a populist message on the economy, and have met individually with former Sen. John Edwards in attempts to win his endorsement.