"This is a war entirely at our disposal to bring to a conclusion given our military power. If we really cared about it, it could have been over and done with by now," Donnelly said.
Recent polls show a strong majority of Americans approve of Obama's handling of national security issues and foreign affairs. But on Libya he has not had significant support from either side of the political spectrum.
Forty percent of Americans oppose U.S. military involvement in Libya, and among those, 65 percent disapprove of his handling of the situation so far, according to an ABC News/Washington Post poll conducted last month. Some conservatives think Obama should have been more aggressive in using force to oust Gadhafi.
For his part, Obama has sought to take a backseat in the Libyan intervention, stressing the U.S. holds a support role as part of an international coalition led by NATO.
"We cannot prevent every injustice perpetrated by a regime against its people, and we have learned from our experience in Iraq just how costly and difficult it is to impose regime change by force -- no matter how well-intended it may be," Obama said Thursday in a speech on Middle East policy.
"But in Libya, we saw the prospect of imminent massacre, had a mandate for action, and heard the Libyan people's call for help. Had we not acted along with our NATO allies and regional coalition partners, thousands would have been killed."
Still, nearly four years ago, it was then-candidate Obama who suggested an end didn't justify the use of any means.
"No more ignoring the law when it's inconvenient. That is not who we are," Obama said, referring to his predecessor President George W. Bush. "We will again set an example for the world that the law is not subject to the whims of stubborn rulers."