With Republican rivals Rudy Giuliani and John McCain skipping a major straw poll in Iowa this Saturday, most presidential political observers say Mitt Romney needs to win big. Saturday's Iowa straw poll is a major test for Romney, because it's a socially conservative state, and if he can win over voters there, it may show his abortion stance can win over conservative voters nationwide.

Mitt Romney has faced criticism on some of the more moderate to liberal positions he stood for as governor of Massachusetts. But now, he is coming clean on one of the more important issues among conservatives. The issue is abortion, and this week he gave his most candid response to date.

"The greatest mistake was when I first ran for office, being deeply opposed to abortion but saying I support the current law, which was pro-choice and effectively a pro-choice position - that was just wrong," said Romney.

Many of the second tier Republican challengers are turning up the heat on all the front-runners on socially conservative issues like abortion.

This week, the former New York mayor had to endure a story that took the online community by storm. Giuliani's daughter, Caroline, had an online entry that indicated she was a member of Barack Obama's Facebook group. The Giuliani campaign said the entry was put on Facebook before the campaign began, and Giuliani said he would not bring his family into the campaign.

Giuliani, in addition to family matters, said this week that his religious beliefs are out of bounds. He refused to answer whether he is a practicing Catholic, but said that while he is pro-choice, there is common ground on the controversial issue of abortion.

On the Democratic side, John Edwards and Barack Obama are going after front-runner Hillary Clinton on the issue of corporate interests and the influence of lobbyists and their cash. Barack Obama has been touting his promise not to take money from DC lobbyists. He says candidates who are comfortable with the role of lobbyists in this country have been in Washington too long. Obama says he accepts lobbyists' legitimate role in Washington, but says they now hold too much power.

John Edwards criticized Hillary Clinton for taking more than $20,000 in donations from News Corp. officials. News Corp. owns Fox.

John Edwards isn't just taking on Hillary Clinton. He says he has the experience to take on corporate America in a way that Barack Obama doesn't.

John McCain, who has had a rough summer so far, will sit down this morning with NBC Today Show's Matt Lauer. Former Secretary of State Colin Powell gave the McCain campaign a $2,300 donation. That is the most that can be given to a candidate in the primaries. A formal endorsement may come in the month ahead.

The Arizona senator is also the only top tier candidate in either party to commit to Spanish-language Univision Network's upcoming historic presidential forum.