U.S. Homeland Security Secretary Janet Napolitano is resigning amid Republican criticisms that accused her of “a consistent disrespect for the rule of law.”   Napolitano announced on Friday that she is stepping down for a senior post at the University of California. Her resignation caught several U.S. officials by surprise as she was seen as a potential successor to U.S. Attorney General Eric Holder.   Meanwhile, Republicans severely criticized Napolitano for her immigration policies.   Sen. Jeff Sessiohns (R-Ala.) said Napolitano’s performance was marked “by a consistent disrespect for the rule of law,” adding “the most significant obstacle to immigration reform remains President Obama's selective enforcement of the law.”   Under Napolitano, the U.S. Department of Homeland Security bought over 1.5 billion rounds of hollow point bullets in 2012 and 360,000 rounds this year for law enforcement officers.   Last month, Napolitano also downplayed the revelations about spying programs run by the U.S. National Security Agency, and denied “an Orwellian State” in the U.S.   “I think people have gotten the idea that there’s an Orwellian state out there that somehow we’re operating in. That’s far from the case,” she said.   In a statement, U.S. President Barack Obama thanked Napolitano for her performance under his presidency.   “At the Department of Homeland Security, Janet’s portfolio has included some of the toughest challenges facing our country. She’s worked around the clock to respond to natural disasters, from the Joplin tornado to Hurricane Sandy, helping Americans recover and rebuild,” he said.   Obama also said the American people “are safer and more secure thanks to Janet’s leadership in protecting our homeland against terrorist attacks.”   Napolitano, a former governor of Arizona, was the third person to lead the DHS, which was created after the 9/11 attacks more than a decade ago. She was appointed by Obama in 2008.