(CNN) -- On the third night of their national convention, the Democrats on Wednesday will turn their focus to a potential weak spot for Sen. Barack Obama: foreign policy.
Sen. Joe Biden of Delaware is set to accept his party's nomination for vice president Wednesday.
Democrats also will officially nominate their presidential ticket and yield the podium to former President Clinton and the presumptive vice presidential nominee, Sen. Joe Biden of Delaware.
The lineup of speakers for Wednesday evening -- with the theme of "Securing America's Future" -- features a roster of Democratic foreign policy and national security heavyweights.
Biden will be leading the attack on Republican Sen. John McCain's foreign policy. In his acceptance speech, Biden is expected to outline why he believes McCain's and President Bush's worldviews have ignored the most dangerous threats facing the United States, said a Democratic source involved in crafting the speech for the six-term senator.
Biden, chairman of the Senate Foreign Relations Committee, widely is believed to have been chosen for the Democratic presidential ticket based on his foreign policy credentials. The Forum: What's your view on national security?
The vice presidential candidate also will focus heavily on his personal biography and Senate experience during his speech, the source said.
Biden will talk about his humble upbringing in Scranton, Pennsylvania, and the lessons he learned growing up in a working-class family, the source added.
In his prime-time address, Biden will hit McCain, a longtime Senate colleague, hard on a wide range of issues, arguing that the senator from Arizona represents four more years of Bush administration policies, the source said.
Others who will speak on foreign policy include former Secretary of State Madeleine Albright; Sens. Evan Bayh and Jack Reed, who are members of the Senate Armed Services Committee; New Mexico Gov. and former U.N. Ambassador Bill Richardson; retired Army Lt. Gen. Claudia Kennedy; and Iraq war veteran Tammy Duckworth.
U.S. Rep. Chet Edwards of Texas, the only House member to be seriously vetted as a potential running mate by the Obama campaign, is expected to discuss veterans' issues. Also addressing the convention: Sen. John Kerry, the 2004 Democratic presidential nominee and a member of the Senate Foreign Relations Committee.
Obama's perceived weakness to McCain on foreign policy and national security issues has been a concern to Democratic strategists, especially since Russia's conflict with Georgia intensified this month.
According to a new CNN/Opinion Research Corp. poll, 78 percent of registered voters said they believe McCain can handle the responsibilities of commander in chief, while 58 percent said they thought Obama could shoulder those responsibilities. View poll results on national security »
The poll, conducted Saturday and Sunday, also found that 60 percent of voters said they believe McCain would better handle the issue of terrorism, whereas 36 percent have more faith in Obama. A majority also said it believes McCain is more likely than Obama to be a strong and decisive leader.
McCain is trying to blunt any momentum Democrats can generate from their convention, in part by pressing his stand on national security issues. His campaign released a new ad Tuesday raising the specter of potential national security crises. It then shows a clip of Sen. Hillary Clinton during the primaries in which she says she knows that "Sen. McCain has a lifetime of experience that he will bring to the White House. And, Obama has a speech he gave in 2002."
Obama has responded to critics of his preparedness on foreign policy and national security by selecting Biden as his running mate. Delaware's senior senator is expected to be nominated for vice president by acclamation, followed by a 20-minute acceptance speech at Wednesday evening's close.
Finally, Wednesday also will witness a continuation of the drama surrounding the Clintons and their role in Obama's Democratic Party.
Bill Clinton is expected to speak before the convention shortly after 9 p.m. ET. Sources told CNN earlier this week that the former president was unhappy with his assigned speech topic for the convention, national security. He reportedly would have preferred to discuss the economy -- the issue that, more than anything else, helped propel him to the White House 16 years ago.
Controversy also surrounds the role of Hillary Clinton's nearly 1,700 pledged delegates. It is believed that Clinton has reached an agreement with the Obama campaign to allow some delegates to cast votes for her before a motion is offered to cut the roll call short and nominate Obama by acclamation. It remains to be seen, however, whether some Clinton delegates will try to start a roll call floor demonstration that may prove embarrassing to convention organizers.
Clinton has strongly urged her supporters to support Obama, but some appear to be backing McCain in growing numbers. A CNN poll taken at the end of June indicated that 16 percent of Clinton's supporters intended to vote for McCain.
A new CNN poll, conducted Saturday and Sunday, showed that 27 percent of her voters now said they supported the Republican candidate.
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