Here are some ways the Republican and Democratic nominating contests could unfold. Try adjusting the sliders to see how the outcomes change. Each line in the chart represents one possible outcome.

Donald J. Trump could lock up the nomination in June, according to our estimate of each candidate’s support in the congressional districts that have yet to vote.

Donald J. Trump transcended regional and ideological divisions on Super Tuesday, winning sweeping victories across the South and in New England. Republican rules allowing states to allocate their delegates on a winner-take-all basis beginning March 15 offer an opportunity for the other candidates to make up ground, but also allow Mr. Trump to extend his lead.

This interactive delegate calculator uses each state’s delegate allocation rules, along with estimates of how favorable each district is for each candidate. To compute these estimates we used a model based on polling, demographics and the results in the past primaries and caucuses.

If Marco Rubio and John Kasich dropped out after March 15, Ted Cruz would need 75 percent of the vote to secure the nomination before the convention.

In this scenario, Mr. Cruz would need to win about of 75 percent of the votes to win enough delegates to secure the nomination.

If Mr. Trump’s share remained around 40 percent, neither candidate would reach the delegate threshold to win the nomination, and the fight would move to the convention floor in July.

After losing every state on Saturday, the one-on-one scenario looks dire for Mr. Rubio – even if he wins Florida on March 15.

If Mr. Rubio would face Mr. Trump one-on-one after March 15 and then continue to win other states with an average of 75 percent of the vote, he would not reach enough delegates to secure the nomination.

This is true even if he wins his home state of Florida.

If Hillary Clinton keeps winning with similar margins, securing the nomination would be unlikely for Bernie Sanders.

It is becoming increasingly difficult for Mr. Sanders to close the delegate gap with Mrs. Clinton. To catch up, he would need to win the remaining races with an average margin of 4 percent. There are no winner-take-all states in the Democratic contest. Delegates are awarded proportionally by congressional district.