A quick comparison of the two fields makes that obvious. The graphs below use the latest Real Clear Politics polling averages for each party's race, which means that they may not track with the latest, hottest poll. And it means that the Democratic field includes Elizabeth Warren (who has said a bajillion times that she isn't running) and Vice President Biden (who has offered no indication that he is).
Clinton is up big, even if you don't look at the scale on the vertical axis.
But what does this mean in terms of support from actual voters? How do Sanders and Fiorina and Christie compare in terms of the number of people who are willing to actually vote for them?
To answer that, we need to know two numbers: How many voters there are and how they break on party lines. To the first point, we can look at Michael McDonald's U.S. Elections Project, which estimated the size of the voting-eligible population at 227 million for last year's election. In 2012, 58 percent of eligible voters voted, so let's say that there are about 132 million voters in the United States who will vote in next year's general. (It will probably be higher, but it doesn't really matter, for reasons that will shortly become obvious.)
The split by party we can get from Gallup: 45 percent of Americans identify as Democrats or independent-leaning-Democrats. Forty-two percent identify as Republicans or lean-Republicans. These numbers fluctuate, sometimes widely. After the 2014 election, there were more identified Republicans, for example. If we use those latest numbers (from early this month) and apply those percentages to the 132 million, and then break out the percentages of support for each candidate in each party, we get a list of support that looks like this.
(That's why the exact count of voters doesn't matter much: We're just looking at overlapping percentages, so the bars will always be the same.)
Sanders, because he has a higher percentage of support in a slightly bigger pool of people, has more on-the-ground support at this moment than Christie or Ben Carson or Rick Perry. He has more than Fiorina, John Kasich, Bobby Jindal and Lindsey Graham combined.
There are a lot of reasons for this and a lot of caveats. The reasons: Fewer Democrats means a higher percentage for the likely candidates (except poor ol' Martin O'Malley, who trails everyone by a bajillion-to-the-bajillion power). The caveats: margin of error, for one. Plus, as Republicans drop out, support will coalesce around the remaining candidates. Although, the same holds for Sanders. When Quinnipiac dropped Warren from its polling, Sanders benefited.
Sanders won't be the Democratic nominee. And neither Fiorina, Kasich nor Graham are likely to be the GOP nominee. Among Americans at large, though, Sanders has a lot more supporters than any number of the often-talked-about Republicans.