The word lively in our headline may understate things. That's particularly true on the Republican side, where business mogul Donald Trump -- who hasn’t held political office -- leads a four-man field. As this week began, he had won nominating contests in 12 states, twice as many as Sen. Ted Cruz of Texas. Sen. Marco Rubio of Florida won only in Minnesota and Sunday in Puerto Rico. Gov. John Kasich of Ohio, the other Republican still in the race, hasn’t come out on top anywhere yet. Although he's far ahead among his party’s candidates, Trump "is reviled not only by Democrats, but also by many prominent Republicans, and has less government experience than any president in history," as New York Times columnist Nicholas Kristof wrote last week.

On the Democratic side, former Secretary of State Hillary Clinton has more nominating delegates so far than Sen. Bernie Sanders of Vermont. She has won in 11 states and he finished first in eight, including Maine on Sunday. As this week starts, both are seeking votes in Michigan, where each party has primaries Tuesday. (Mississippi also votes then.) Clinton lived in the White House from 1993-2001 as the wife of President Bill Clinton, who now campaigns actively for her.

This primary and caucus season, which runs until June 14, picks delegates pledged to vote for specific candidates at each party’s national conventions this July, as the video below explains. Public and media attention are captivated by Trump’s feisty, unorthodox candidacy. With the slogan "Make American Great Again," he talks brashly about banning Muslim immigrants, building a wall at the border with Mexico and why "we should go for waterboarding [torture] and we should go tougher than waterboarding" of terrorists. A day after he did well in last week's delegate-rich "Super Tuesday" contests, New York Times columnist Gail Collins wrote: "Donald Trump was made for a world of Twitter and YouTube." A news article in her paper notes: "He is in a strong position to be the Republican presidential nominee, a prospect that less than a year ago seemed inconceivable. The political world has gone through stages of disbelief about his candidacy since he announced it last June: dismissing it at first, then acknowledging his strength and finally accepting that he could win the nomination."

Donald Trump says: "Every country who does business with the United States takes advantage of the United States." – At Maine rally, March 3

Broadcaster says: "Tonight [March 1] may well mark the consolidation of Trump's hold on GOP nomination. The media both missed this story and actively made it possible." – David Folkenflik, National Public Radio correspondent

Past Republican candidate says: "Donald Trump lacks the temperament to be president. . . . Dishonesty is Donald Trump's hallmark. . . . He's playing the members of the American public for suckers." – Mitt Romney, who ran against Barack Obama in 2012, in March 3 speech