Vermont Senator Bernie Sanders scored a surprise victory Tuesday in the northern state of Michigan, defeating former Secretary of State Hillary Clinton in the state's Democratic presidential primary.
Many polls showed Clinton heavily favored to win the state, but Sanders got enough votes for a narrow win. Clinton did easily win the other Democratic primary held Tuesday in the southern state of Mississippi.
Sanders said the Michigan victory means his "political revolution" is strong across the country, and that he believes the areas where his campaign is strongest are the ones that have not yet voted. He highlighted his message against corrupt campaign financing, an unfair economy and broken criminal justice system.
Clinton told voters in Cleveland, Ohio -- one of the five states holding a Democratic primary next week -- that she is proud of the campaign she and Sanders are running. She compared it to the Republican campaign, where she said the candidates are tearing each other down.
In the Republican race, businessman Donald Trump won by large margins in both Michigan and Mississippi, while Florida Senator Marco Rubio finished a distant fourth place in each race. Republicans also competed in Idaho and Hawaii.
The usually plain-speaking and often harsh Trump was uncharacteristically subdued in thanking voters for their support, but he mocked Cruz, who has called himself the only candidate who can beat Trump.
Republican leaders have launched an intense effort to try to stop Trump, saying he is too unpredictable and would lose in November if Clinton is the Democratic nominee. Trump dismissed efforts to stop his campaign, saying: "It shows you how brilliant the public is."
Several anti-Trump organizations plan to spend at least $10 million in the next week on television advertisements, primarily in Florida and Illinois, two big states where Republicans are holding primaries on March 15.
Rather than respond to the ad campaign against him with television ads of his own, Trump said he would continue attacking his opponents through Twitter.
"We cannot let the failing Republican establishment, who could not stop Obama, ruin the movement with millions of dollars in false ads!" Trump said Monday.
For the Democrats, Clinton has a large lead in the delegate count over her only rival, Vermont Senator Bernie Sanders.
Sanders enjoys wide support among young voters and has appealed to them not to stay home on election day.
One-hundred-50 Republican delegates are up for grabs in all four states Tuesday. The Democrats have 189 delegates at stake.
The delegates and their pledges of support are the key to securing the party's nomination at this July's conventions.