The man charged with bringing order to Donald Trump’s chaotic campaign for president has accused the millionaire’s main Republican rival, Ted Cruz, of “Gestapo tactics”, a day after Trump failed to win a single elected supporter at the Colorado state convention.

“You go to these county conventions and you see the Gestapo tactics, the scorched-earth tactics,” said Paul Manafort, Trump’s newly appointed “convention manager”, in an interview with NBC’s Meet the Press on Sunday.

Manafort was not specific about what Cruz, the Texas senator who is best placed to take on Trump, or his campaign had done to remind him of the Nazi secret police.

“We’re going to be filing several protests because the reality is, they are not playing by the rules,” he said. “If they don’t get what they want, they blow it up. That’s not going to work.”

Trump still leads Cruz in the race to secure the Republican nomination, which requires 1,237 delegates at the party’s convention in Cleveland in July. But Cruz has organized well with local conservatives and state leaders loathe to see Trump as their nominee.

In contrast to the way Cruz’s team has managed the messy local politics of Colorado and Louisiana, Trump’s campaign has become a picture of gilded chaos: wild and sometimes violent rallies, outrageous and contradictory claims on Twitter and TV, and a campaign manager charged with battery against a reporter.

In Colorado, the Trump campaign put out mislabelled ballots and would-be delegates made such pitches for support as “Donald Trump! Buy Colorado weed!”

Manafort said: “I acknowledge that we weren’t playing in Colorado and they did.”

On Sunday, Trump himself accused Cruz’s campaign of bribing delegates, apparently in an allusion to Louisiana, where Cruz gained delegates through local politics despite Trump having won the state’s primary.

The reality is, they are not playing by the rules. If they don’t get what they want, they blow it up Paul Manafort

“I win a state in votes and then get non-representative delegates because they are offered all sorts of goodies by Cruz campaign,” he tweeted. “Bad system!”

The businessman hired Manafort to reorganize his campaign, hoping to draw on the aide’s experience in helping Gerald Ford win a contested convention against Ronald Reagan in 1976.

Manafort has since advised Viktor Yanukovych, the twice-ousted former leader of Ukraine, and Ferdinand Marcos, the former dictator of the Philippines. Though Cruz has a poor chance to defeat Trump outright, if he can prevent the businessman from getting 1,237 delegates, he will stand a better chance of rallying anti-Trump Republicans to his campaign.

Manafort insisted that Trump will do well in New York, which votes on 19 April and has 95 delegates at stake for Republicans, and in east coast states to which candidates of both parties have flocked ahead of April elections.

The Democratic contest also took on an increasingly personal tone over the weekend, as Bernie Sanders and Hillary Clinton campaigned in New York, where the former grew up and the latter set down roots. In his native borough, Brooklyn, Sanders sharpened his criticisms of Clinton.

“In terms of her judgment, something is clearly lacking,” the senator told NBC on Sunday, alluding to Clinton’s support for free trade agreements and her reliance on donations from Wall Street.

But the senator repeated that he would support Clinton as the nominee against any Republican, telling CNN: “We will do everything possible to prevent this country from seeing a Donald Trump or some other Republican in the White House.”

Clinton did not deign to attack her rival ahead of their New York debate this Thursday.

“I don’t have anything negative to say about him,” she told CNN’s State of the Nation. “I’d take him over Donald Trump or Ted Cruz any day.”

The former secretary of state, confident in her big lead in delegates and superdelegates, instead shifted toward the general election and faced questions about the legacy of crime and poverty that many say her husband created as president in the 1990s.

Earlier this week, protesters confronted Bill Clinton at a rally in Philadelphia, criticizing him presiding over a huge increase in the number of black people sent to prison, and for his wife’s use of the term “super-predator”.

Bill Clinton confronts protesters in Philadelphia. Guardian

On Sunday, Clinton defended her husband. “There were a lot of people very scared and concerned about high crime back in the day, and now we have to say, ‘OK, we’ve got to deal with the consequences,’” she said, acknowledging that too many people were in prison.

She also received an unexpected boost from Barack Obama, who gave his first interview to Fox News in more than two years. The president defended Clinton over accusations that she compromised national security through her use of a private email server.

“There’s a carelessness in terms of managing emails that she has owned,” he conceded, before stressing: “She would never intentionally put America in any kind of jeopardy.”

“This is somebody who has served her country for four years as secretary of state, and did an outstanding job,” he added.