Democratic presidential candidate Bernie Sanders speaks during a rally at Bon Secours Wellness Arena in Greenville, S.C., on Sunday. (Photo by Cassi Alexandra/For The Washington Post)

BOSTON -- 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 Vermont senator drew distinctions with Clinton on campaign finance and trade -- two 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 on Saturday in the Nevada caucuses and in advance of an expected loss Saturday in the South Carolina primary, in which polls have showed Clinton with a comfortable lead.

With 11 other states holding nominating contests on 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 populations 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 on Monday, spending a second day in California at a series of high-dollar fundraisers.

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

For the first months of his bid, he barely mentioned the Democratic frontrunner. 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, however, 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 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 asserted the two candidates have “a very profound difference” on campaign finance, noting that a super PAC supporting Clinton had 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. In debates and in other appearances, Clinton has argued that she is not influenced by the donations and in fact has developed strong proposals to better police Wall Street.

Sanders seemed to be mocking her at his news conference.

“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. “That is what every candidate who has received special interest money always says.”

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

Left unmentioned were a couple of outside groups that are supporting Sanders, including a national nurses union. Sanders previously has said the group is different than super PACs supporting other presidential candidates because it was not established to back him and its funding comes from its membership rather than a limited number of wealthy donors.

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.

“If I am elected president, I will not support the TPP,” Sanders said.

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,” Sander said.

He then chided reporters for placing too much emphasis on the importance of each nominating contest, noting 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 wound up winning 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 the race with Clinton will “a slog” fought “state by state by state.”

People’s Politics, the group that endorsed Sanders, bills itself as a new national grass-roots organization of “everyday people fighting for racial and economic justice.”

“We are black, Latino, Asian, white working class, documented and undocumented, women and men, rural and urban,” the group says in promotional literature. Member organizations include groups based in several northeastern states as well as Illinois, Iowa and New Mexico.