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Nearly 70 percent of Americans say they lack confidence that the U.S. will achieve its goals in fighting the terrorist group ISIS, according to a new NBC News/Wall Street Journal/Annenberg poll. The findings come in the wake of President Barack Obama’s national address announcing new measures to combat the Sunni militants.

Pressure is mounting on the U.S. and its allies to cripple the militants, who have waged a brutal campaign across Syria and Iraq. ISIS already has beheaded two American journalists and on Saturday released a video showing the execution of a third Westerner, British aid worker David Haines.

The poll – conducted before the latest execution emerged – showed that a combined 68 percent of Americans say they have “very little” or “just some” confidence that Obama’s goals of degrading and eliminating the threat posed by ISIS will be achieved. Just 28 percent said they had “a great deal” or “quite a bit” of confidence. Still, 62 percent of voters say they support Obama’s decision to take action against ISIS in Iraq and Syria, while 22 percent oppose it.

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“The bottom line: The president has made his case to the American public, and like other presidents who faced war and peace issues, support usually follows,” said Democratic pollster Peter Hart, who helped conduct the survey. “The difference in this military encounter is that, right out of the box, Americans are skeptical if this will work.”

The poll also shows that 38 percent of voters approve of Obama’s job in handling foreign policy.

A separate survey that re-contacted respondents from last week’s national NBC/WSJ poll after the president’s speech found a slight increase in the percentage of Americans who believe that military action against ISIS is in the nation’s interest, with a rise to 68 percent from 65 percent.

In addition, 26 percent of those re-contacted said that Obama’s speech on Wednesday had given them a more favorable impression of the president. Another 20 percent had a less favorable opinion and 53 percent said it made no difference.

The latest NBC/WSJ/Annenberg poll of 554 registered voters was conducted September 11-13. It has a margin of error of plus-minus 5.5 percentage points. The NBC/WSJ re-contact survey was conducted Sept. 11-13 of 207 re-contacted voters.