Tuesday’s Democratic Party primary states are unusually favorable for Hillary Clinton. The left side of the graph above shows Democratic polling percentages, weighted by the number of delegates. On the right are national poll medians. Where possible, the data come from poll samples of February 22 or later.

Clinton’s Super Tuesday margin is about 15 percentage points better than her national margin. A number of states should come in very strong for her: Alabama, Arkansas, Georgia, Minnesota, Tennessee, Texas, and Virginia. She leads in these states by margins of 20 to 35 percentage points. Most are Southern states, where Clinton benefits from a considerable black vote (of which she won an amazing 86% in South Carolina). Big wins matter, since Democratic convention delegates are assigned close to proportionally to vote share.

However, proportional representation of votes does not mean that Sanders or Clinton needs 50% of the overall vote to get the nomination. There are also superdelegates, who comprise about 10% of all delegates; nearly all of them are committed to Clinton. If they were to stick with their current commitment, Sanders would need about 56% of the national popular vote to be headed for a majority at the convention. Sanders has a tall hill to climb. In contrast, Clinton would only need 44% of the popular vote.

(In comments, several of you think that if Sanders were to get a clear majority of pledged delegates, the superdelegates would come under considerable pressure to change their allegiance. That is possible – but hard to estimate. Practically speaking, I think that Clinton’s popular-vote requirement is somewhere between 44% and 50%, but we don’t know where. I note that if pre-election polls are accurate, we will never learn the answer to this question.)

For those of you who think this is an unfair advantage for Clinton, keep in mind that on the Republican side, Donald Trump’s advantage is larger. In a divided field, he only needs 30% of the popular vote on Super Tuesday to end up with a majority of the cumulative delegates. So even though Trump has a much smaller share of support in the Republican primaries than Clinton does in the Democratic race, the two candidates are in fairly similar competitive positions.

Sanders’s one big expected win on Tuesday is Vermont (Sanders 82%, Clinton 12%). To be competitive for the nomination, in other states Sanders needs to do about 10 percentage points better than indicated by polls. That would involve winning Massachusetts (currently Clinton 49%, Sanders 44%, median of 3 polls) and narrowing Clinton’s wins elsewhere to 10-20 percentage points. However, if the polling numbers above turn out to be accurate, Clinton will have a great day – and a clear path to the nomination.