Washington CNN —  

Bernie Sanders’ potential upset of Hillary Clinton in the Iowa caucuses is raising alarms for a former strategist to the last candidate to beat her there, Barack Obama.

David Plouffe, who helped engineer then-Senator Obama’s 2008 victory in Iowa – and later the presidency – on Sunday jabbed at Sanders on several fronts. In a tweet, Plouffe questioned Sanders’ late hour Hawkeye State campaigning with Cornel West, a Princeton professor of African-American studies who has often been critical of Obama. It’s a sensitive point for Obama partisans since the President’s victory over Clinton for the 2008 Democratic nomination was launched in Iowa, an overwhelmingly white state.

“Sanders closing with Cornel West and embracing idea of Buyer’s Remorse with @POTUS. Be honest then Senator - run firmly against Obama record”

Plouffe, via a post on Medium, endorsed Clinton in October.

Then in a tweet hours later Plouffe hit the Vermont senator for writing a front cover blurb on a book, by Bill Press, about how Obama’s seven-year tenure in the White House has been a let-down for progressives – “Buyer’s Remorse: How Obama let Progressives Down.”

“Lending your name & endorsement to this critique is no small thing in the heat of an election to replace Pres Obama.”

Neither tweet mentions Hillary Clinton by name. Obama himself is officially neutral in the primary fight to succeed him.

The tweets from Plouffe, now an executive at Uber, come as polls show Clinton and Sanders in a tight race on the eve of the Iowa caucuses, which kick off presidential voting. The Des Moines Register/Bloomberg Politics Iowa Poll, released Saturday evening, found Clinton holding a narrow lead over Sanders, 45% to 42%.

Asked Sunday on NBC’s “Meet The Press” about the “Buyer’s Remorse” book blurb, Sanders said the economy has improved under Obama.

“What we have got to do is to involve people in the political process in a way that we have not done. The reason that the rich get richer, everybody else gets poorer, is big money controls what goes on in Congress. The answer though to that is a political revolution involving people in the political process,” Sanders said.