A prominent Democratic campaign firm announced Monday that it is launching a super PAC to back California Sen. Dianne Feinstein after her reelection bid was challenged by a fellow Democrat.&ldquo;We see the highest-ranking woman in the U.S. Senate under attack by political opportunists, and we are determined to fight just as hard for her as she fights for California,&rdquo; said Sean Clegg, a partner at SCN Strategies, which represents Gov. Jerry Brown, Sen. Kamala Harris, Lt. Gov. Gavin Newsom and others.Donors can contribute unlimited amounts to a super PAC, which cannot coordinate with a candidate&rsquo;s campaign.The San Francisco group announced the formation of the &ldquo;Fight for California&rdquo; super PAC one day after Democratic state Senate leader Kevin de Le&oacute;n announced he would challenge Feinstein, and on the same day a pro-De Le&oacute;n super PAC was launched.De Le&oacute;n faces many hurdles in challenging Feinstein, a decades-long fixture in California politics. Among the most pressing is money.De Le&oacute;n lacks the donor base of other candidates who have run for statewide office. The nearly $3 million he has in state campaign accounts can&rsquo;t be used in a federal race. He does&nbsp;enjoy support from donors&nbsp;because of his leadership role, but they may be reluctant to open their wallets and anger Feinstein.