Democratic presidential candidate, Sen. Bernie Sanders (Vermont) at a rally Monday at the University of Massachusetts in Amherst. (Matthew Cavanaugh/Getty Images)

Democratic presidential hopeful Bernie Sanders opened a new phase of his campaign Monday, pledging to more aggressively lay out his differences with Hillary Clinton, an opponent whose views on some issues, he said, are guided by “hastily adopted campaign rhetoric.”

Speaking at a news conference here, the senator from Vermont drew distinctions with Clinton on campaign finance and trade — the start of what he said will be a series of differences detailed in coming weeks — and pledged to contest the Democratic nomination through the convention.

“I have to say that I am delighted that Secretary Clinton, month after month after month, seems to be adopting more and more of the positions that we have advocated,” Sanders said, adding that the former secretary of state “is beginning to use a lot of the language and phraseology that we have used.”

The feistier performance by Sanders comes on the heels of his loss to Clinton in the Nevada caucuses Saturday and in advance of an expected loss this Saturday in the South Carolina primary, in which polls have shown Clinton with a comfortable lead.

Bernie Sanders denies Hillary Clinton's claims that he's a "single-issue candidate." Here's why his opponents say he needs to branch out. (Peter Stevenson/The Washington Post)

With 11 other states holding nominating contests March 1, Sanders is fighting to show that he is not running out of momentum after strong performances in the first two contests, in Iowa and New Hampshire, where the voters were largely white.

He chose to hold his news conference in Massachusetts, one of the Super Tuesday states where he appears strongest against Clinton. Sanders also unveiled an endorsement from a new multi-state, racially diverse coalition of progressive groups called People’s Politics.

Clinton held no public campaign events Monday, spending a second day in California at a series of high-dollar fundraisers.

Earlier Monday, Sanders campaigned in South Carolina, where, during a stop in Sumter, he sought to push back against Clinton and other critics who have said that his agenda is utopian and unachievable.

In recent weeks, Clinton has cast herself as the more pragmatic candidate who could implement a progressive agenda while arguing that Sanders’s plans for universal health care and other bold policies would never be implemented.

Sanders countered, saying, “One of the things that is going on in this campaign is that Bernie Sanders is too ambitious, he’s thinking too big. Well, I don’t think so. I mean virtually every idea that we are bringing forth not only is the right idea, it’s what our country needs, it’s what the American people want.”

Sanders, a self-described democratic socialist, ticked off some of his proposals, including ushering in a “state-of-the-art, cutting-edge child-care system,” each time telling his audience that the idea wasn’t as “radical” as it’s been portrayed.

As a presidential candidate, Sanders has toggled back and forth a couple of times when it comes to drawing contrasts with Clinton.

For the first months of his bid, he barely mentioned his opponent. Last fall, however, he considerably stepped up his efforts to draw policy distinctions, and during the first part of the year, he was openly critical of Clinton’s acceptance of large speaking fees from Goldman Sachs and other Wall Street interests.

More recently on the campaign trail, Sanders had returned to only infrequent mentions of the former secretary of state, even as she and her surrogates attacked him on a range of issues, including gun control, immigration and women’s reproductive rights.

The issues Sanders chose to highlight during his news conference Monday were not new ones, but his critique of Clinton was more pointed.

“The people of Massachusetts and the people of the United States need to know that difference between hastily adopted campaign rhetoric and the real record and the long-held ideas of the candidates,” he said.

He asserted that the two candidates have “a very profound difference” on campaign finance, noting that a super PAC supporting Clinton raised $15 million from Wall Street interests during the most recent reporting period.

Clinton has sought to distance herself from the donations, saying they were to a super PAC originally established to support President Obama but has since chosen to back her.

“I know that every candidate who has ever received special-
interest money always says that the millions and millions of dollars they receive will never influence them — never, never, never,” he said.

Sanders sought to contrast his method of fundraising, saying his campaign has received 4 million donations averaging $27 apiece, most of them online.

Sanders also highlighted his long record in Congress opposing trade deals, including the pending Trans-Pacific Partnership, a deal being pushed by Obama.

After declining to take a position on the pact for months, Clinton announced her opposition far more recently. At his news conference, Sanders shared comments made in January by Tom Donohue, president of the U.S. Chamber of Commerce, predicting Clinton would eventually support the deal if she won the Democratic nomination. Sanders later opened the floor to reporter’s questions, answering two before he said he had to leave to make it to a scheduled rally in Amherst.

The first dealt with whether he has a viable path to the Democratic nomination. “The short, three-letter answer is Y-E-S,” Sanders said.

He then chided reporters for placing too much emphasis on the importance of each nominating contest, noting that the primaries and caucuses are not winner-take-all and saying he is in the race for the long haul.

In Nevada, Sanders said, Clinton won 19 delegates to the national convention, while he received 15. (An updated count released Monday put the tally at 20 to 15). It takes about 2,400 delegates to secure the nomination, Sanders said. He predicted that the race with Clinton will be “a slog” fought “state by state by state.”