It was a huge Super Tuesday primary night for Hillary Clinton, who cleaned up in Florida, North Carolina, Illinois and Ohio against Bernie Sanders, who nevertheless isn't inclined to fade into the woodwork. It was a particularly welcome string of victories for Clinton who took her defeat hard to Sanders days earlier in Michigan.

Sanders had hoped to repeat his victory in the industrial Midwest but failed to beat Hillary in hard-fought Ohio, despite his heavy spending and focus there — and had been optimistic about Illinois and Missouri as well.

The Ohio win was especially sweet for the Clinton campaign crew who fine-tuned their candidate's message to appeal more strongly to heartland Americans still struggling with the economy, which has more naturally been Sanders' constituency.

Sanders is so far sticking with the race, though Clinton looks more than ever like a locomotive heading for the general election as the Democratic nominee. Her 300-delegate lead over Sanders now is three times higher than Barack Obama's margin was over her at this point in their race for the Democratic nomination in 2008, notes the New York Times.

"We are moving closer to securing the Democratic Party nomination and winning this election in November," she crowed in her victory speech to cheers from a supportive crowd of hundreds in West Palm Beach, Florida. Clinton was gracious to the beaten Sanders, and again set her sights on the man she believes will be her rival in the general election: Donald Trump.

"Our commander-in-chief has to be able to defend our country, not embarrass it," she said. "When we hear a candidate for president call for rounding up 12 million immigrants, banning all Muslims from entering the United States, when he embraces torture, that doesn't make him strong — it makes him wrong," Clinton said, and called on all Americans to fight against "bluster and bigotry."

Clinton won Illinois with just over a 1% lead over Sanders. She also eked out a two-tenths of a percent lead over her rival (49.6% to 49.4%) in Missouri, but officials declared that race too close to call just yet.

But she crushed Sanders in Florida with a 31-point win (64.5% to 33.3%). And she won North Carolina by a hefty 14-point margin (54.6% to 40.8%), despite a $1m Sanders ad blitz over the past week that tripled her spending there.

But Sanders appeared to be doggedly determined to stick out the race. He again criticised corporate America — and Clinton, singling out her support by a super PAC and her reliance on large donations from well-heeled Americans.

"She has received money from the drug companies and the fossil fuel industry," he said to loud hisses and boos from his hefty crowd of supporters. "She has given speeches on Wall Street for $225,000 a pop."

Sanders' chances look better in the next contests in overwhelmingly white caucus states like Idaho, Utah, Washington, Alaska — and Hawaii in later March — where the candidate could collect some 244 delegates in total.