Arab Spring turmoil evokes political response President Obama vows justice for the killing of four U.S. diplomats Mitt Romney criticizes Obama's foreign policy as weak and conflicted Others stress the nation must support democratic aspirations abroad Protesters attacked U.S. compounds in Egypt and Libya Washington (CNN) -- President Barack Obama and political leaders from both parties stressed resolve and unity Wednesday, after a day of violence in Arab Spring countries killed four American diplomats. Republican challenger Mitt Romney harshly criticized the president's foreign policy as weak and conflicted. The violence Tuesday -- the 11th anniversary of the 9/11 terrorist attacks by al Qaeda on the United States -- included an attack that killed Ambassador Chris Stevens and three other diplomats in Benghazi, Libya, as well as protesters assaulting the U.S. Consulate there and the U.S. Embassy in Egypt. Demonstrations over an anti-Islam video on a U.S. website spread Wednesday to Sudan, and officials warned of possible street protests in Afghanistan after midday prayers Friday. Obama, flanked by Secretary of State Hillary Clinton, hailed the service of Stevens and the other slain diplomats and promised to go after those responsible for their killings. At the same time, the president stressed that U.S. support would continue for the democratic aspirations expressed by Arab Spring uprisings in Libya and Egypt, and that American values of religious tolerance and freedom should be followed around the world. Campaigns focus on foreign policy after attacks We will not waver in our commitment to see that justice is done for this terrible act. And make no mistake, justice will be done," Obama said in the White House Rose Garden. Referring to the video being promoted on anti-Islam websites in the United States, Obama said, "We reject all efforts to denigrate the religious beliefs of others." But there is absolutely no justification for this type of senseless violence. None," Obama said. The world must stand together to unequivocally reject these brutal acts. In her own statement earlier, Clinton asked, "How could this happen in a country we helped liberate, in a city we helped save from destruction?" "This question reflects just how complicated and at times how confounding the world can be," she said. But we must be clear-eyed even in our grief. This was an attack by a small and savage group, not the people or government of Libya. A joint statement by hawkish veteran Sens. John McCain of Arizona, Lindsey Graham of South Carolina and Joe Lieberman of Connecticut also condemned the attacks and called for justice while also expressing support for the mission in both Libya and Egypt. "Despite this horrific attack, we cannot give in to the temptation to believe that our support for the democratic aspirations of people in Libya, Egypt, and elsewhere in the broader Middle East is naive or mistaken," said the statement by the senators, who have been strong critics of Obama for what they have called an unassertive foreign policy. We cannot resign ourselves to the false belief that the Arab Spring is doomed to be defined not by the desire for democracy and freedom that has inspired millions of people to peaceful action, but by the dark fanaticism of terrorists. McCain, the Republican presidential candidate against Obama in 2008, praised Clinton's statement on Twitter, saying it provided "just the right message and tone." Romney, however, sharply criticized the administration Wednesday, saying the U.S. response amounted to sending "mixed messages" on American values and foreign policy to the rest of the world. "I think President Obama has demonstrated a lack of clarity as to a foreign policy," Romney said in Jacksonville, Florida, continuing a line of criticism his campaign began late Tuesday when he issued a statement that labeled the U.S. response to attacks on the Cairo embassy as "disgraceful." Romney camp tries to manage fallout from Libya response "I think it is a terrible course for America to stand in apology for our values," Romney said of a statement by the embassy that condemned the anti-Islam video that fomented protests outside the compound. When our grounds are being attacked and being breached ... the first response of the United States must be outrage at the breach of the sovereignty of our nation. And apology for America's values is never the right course. He said a later White House attempt to distance itself from the embassy statement sent a conflicting message on foreign policy at a time when resolve and clarity were needed, and he made clear he believed the responsibility rested with Obama. "The president takes responsibility not just for the words that come from his mouth but also from his ambassadors, from his administration, from his embassies, from his State Department," Romney said, adding: "They clearly sent mixed messages to the world. ... The statement that came from the administration was a statement which is akin to apology and I think was a severe miscalculation. Democrats quickly fired back that the former Massachusetts governor's comments were inappropriate and misguided. "They demonstrate an insensitivity and a lack of judgment about what is happening right now," Senate Foreign Relations Committee Chairman John Kerry of Massachusetts told CNN, adding: "I don't think he knows what he is talking about, frankly." On Tuesday night, when only one of the diplomats in Libya was known to have been killed, Romney's campaign issued a statement in which he condemned both the assault on the Cairo embassy and what he called the weak U.S. response. "It's disgraceful that the Obama Administration's first response was not to condemn attacks on our diplomatic missions, but to sympathize with those who waged the attacks," the Romney statement said, referring to the initial Cairo embassy statement that was released before protesters stormed the compound. The embassy statement had said it "condemns the continuing efforts by misguided individuals to hurt the religious feelings of Muslims -- as we condemn efforts to offend believers of all religions." "Respect for religious beliefs is a cornerstone of American democracy," the embassy statement continued. Later, Clinton issued a statement that said anger over the film did not justify the violence. "The United States deplores any intentional effort to denigrate the religious beliefs of others," Clinton wrote. But let me be clear: There is never any justification for violent acts of this kind. Romney's statement Tuesday night originally had a 12 midnight embargo, apparently to stick to his previously stated intention to avoid overt politicking on the 9/11 anniversary. The campaign then lifted the embargo before midnight. Obama's campaign responded quickly, saying Romney was using Middle East events for political gain. Obama condemns attacks in Libya "We are shocked that, at a time when the United States of America is confronting the tragic death of one of our diplomatic officers in Libya, Gov. Romney would choose to launch a political attack," Obama campaign press secretary Ben LaBolt wrote. Wednesday's campaign shift to foreign policy comes after months of concerted focus on jobs and the economy, especially by the Romney campaign in its effort to frame the vote as a referendum on Obama's handling of the nation's sluggish economic recovery. Romney generally makes little mention of foreign policy on the stump, and was criticized for not mentioning the war in Afghanistan during his speech accepting the GOP nomination at last month's Republican National Convention. The latest CNN/ORC International survey released earlier this week showed Obama with a 54%-42% advantage over Romney on foreign policy. In Congress, legislators sounded united in their calls for justice and continued efforts to help bring peaceful democratic transitions in Libya, Egypt and elsewhere. "I have seen this amateurish and stupid video, and there is nothing in it -- despite the fact that it is deliberately provocative -- that could ever justify the murder of these innocent people," said Rep. Keith Ellison, D-Minnesota, the only Muslim U.S. legislator. Senate Republican leader Mitch McConnell of Kentucky said he supported "employing every available tool at our disposal to ensure the safety of Americans overseas and to hunt down those responsible for those attacks." "Yesterday we commemorated the anniversary of the attacks of September 11," he added, "and today we are reminded that brave Americans serve us every day at the risk of their own lives." Pro-al Qaeda group seen behind deadly Benghazi attack CNN's Peter Hamby, Elise Labott, Kate Bolduan,Ted Barrett, Brianna Keilar, Dan Lothian and Barbara Starr contributed to this report.