NORTH LAS VEGAS, Nevada — Hillary Rodham Clinton is opposing President Barack Obama's authorization for oil drilling in the Alaska Arctic and his delays on the Keystone XL pipeline, in some of the clearest signs of the Democratic front-runner distancing herself from the president. Having agreed with him on most issues so far in her 2016 race, Clinton edged to Obama's left on climate change on Tuesday. In the course of a few hours, she announced her disapproval of his move to allow Royal Dutch Shell to drill in the Arctic Ocean and her impatience for a decision on the Keystone XL pipeline Alberta in Canada to Texas. Clinton argued on Twitter that the Arctic is a unique treasure and “not worth the risk of drilling.” Then as she took questions from reporters later in Nevada, she said the US should be focusing on cleaner sources of renewable energy, rather than risking “potential catastrophes” in the search for more oil. “I think the very great difficulties that Shell encountered the last time they tried to do that should be a red flag for anybody,” Clinton said, referring to a setback that beset the oil giant when it tried to drill there in 2012, including a rig that ran aground. In the early months of her campaign, Clinton has rarely disagreed publicly with Obama, who remains popular among core Democratic voters but much less so among the broader American public. Her biggest rebuff came in June when she declined to support giving Obama expedited negotiating authority on trade. Even then, she characterized her position as more of a wait-and-see approach than outright opposition to the trade deals he's pursuing. One of Clinton's challenges is winning enough support in the liberal wing of the Democratic Party. Her primary opponents like Vermont Sen. Bernie Sanders are opposed to Keystone, Arctic drilling and other projects deemed risky for the environment. And in recent weeks, Clinton has suggested that she could be more effective than Obama in working with Republicans to get things done. Clinton's comments on Arctic drilling came less than a day after the Obama administration, in a long-expected move, gave Shell the final permits needed to drill for oil off Alaska's northwest coast, drawing consternation from environmentalists. Unsurprisingly, the same groups that had criticized Obama praised Clinton for stating her opposition. “We applaud Secretary Clinton for standing up for what science, the will of the American people and common sense demand,” said Sierra Club Executive Director Michael Brune. Clinton's Republican opponents pushed back. “Wrong,” former Florida Gov. Jeb Bush responded on Twitter. “Being more-anti energy than Obama is extreme.” Clinton has said she won't take a stance on whether to approve the Keystone XL pipeline unless the decision is still pending if and when she's elected. Keystone supporters and opponents alike have questioned her refusal to say what she believes about an issue important to voters. — AP