BLOOMINGTON, Indiana (AFP) - The Democratic race for the White House is tightening ahead of two critical showdowns next week, according to fresh opinion polls that suggest Barack Obama has been damaged by a row over his fiery former pastor. Obama's rival Hillary Clinton meanwhile weighed in on the latest furore over the Reverend Jeremiah Wright's rhetoric, branding his comments offensive, as she drove towards the May 6 primaries in Indiana and North Carolina. A CBS/New York Times poll found 51 percent of Democratic voters believe Obama will be the party's standard bearer against the Republican's apparent nominee John McCain down a whopping 18 points from a month ago. Obama's unfavorable rating among registered voters meanwhile rose from 24 percent a month ago to 34 percent. The poll was conducted between April 25 and 29, during the height of the latest Wright uproar. The Illinois senator still led Clinton 46 to 38 percent among Democratic voters nationwide. But Clinton led McCain 48 percent to 43 percent among all registered voters, while Obama and McCain were tied at 45 percent. An NBC News/Wall Street Journal poll out Wednesday found the rivals still closely matched in a general election fight with McCain. But the percentage of voters who identified with Obama's values had dipped slightly, to 45 percent from 50 percent last month. Obama has endured a tough month, fighting off controversy over his comment that some working class voters are "bitter," losing to Clinton by nearly 10 points in Pennsylvania last week. But he still leads Clinton in nominating contest wins, pledged nominating delegates and the crucial fundraising stakes. Perceptions are crucial to the end-game in the Democratic race, as Clinton tries to convince top party officials, or superdelegates, that her rival would be a liability in the November 4 election. Clinton earlier branded Wright's rhetoric "outrageous," in her most expansive comments yet on the issue. "Well, I take offense," she said in an interview with Fox News Channel. "I think it's offensive and outrageous. I'm going to express my opinion, others can express theirs." Wright once claimed AIDS was a racist government plot, and suggested after the September 11 attacks in 2001 that black citizens sing "God Damn America" to protest their treatment by whites. Local polls support the notion that the Democratic race is narrowing. A Howey-Gauge poll in Indiana, released Tuesday, had Obama up by just 47 to 45 percentage points. Clinton trailed by 15 points in the same poll in February. In North Carolina, Obama led the RealClearPolitics average by 10 points, but a Survey USA poll Tuesday had him up by only five. At a rally in Bloomington, Obama tried to push past the controversy and shift the blame to his opponents. "Because we've been so successful that's why my opponents have been trying to make this election about me lately," he told the roaring crowd. "We're not sure if he shares our values... he has a funny name and says he's a Christian but we're not sure. His former pastor said some terrible things. Can we trust this guy?" "They can't win on the ideas so they want to make the election about my values, my identity, my character." Obama said Tuesday he was "outraged" by Wright's comments after the pastor launched a weekend media tour. Michelle Obama expressed hope her husband's rejection of their former pastor would draw a line under the furore. "Yes, it was painful. Yes, it's been difficult," she told CNN television, adding that her husband's decision to publicly denounce Wright was a "tough thing to do." "I think Barack was so clear and has been so open about this issue," she said, adding: "We're going to close the chapter and move into the next phase of this election." Neither Clinton nor Obama can now reach the 2,025 pledged delegates threshold to claim the Democratic nomination outright in nine remaining nominating contests. So the fate of the party's presidential pick to take on McCain lies in the hands of the nearly 800 superdelegates who can vote how they like at the party's convention in Denver, Colorado on August 25-28.