Not everyone thinks that Bernie Sanders is the best choice
as the Democratic nominee for President. In fact, not everyone who thinks Senator Sanders has the right point of view on issues thinks he is the best choice as the nominee. That may come as a surprise to some people, but it shouldn't. There are some political considerations that lead many Democrats to think Hillary Clinton would be a better nominee. Some of the reasons for that thinking, even among Democrats who strongly support Sanders' positions include:
1. Electability - For many Democrats, policy positions alone are not enough. Some remember outstanding Democratic candidates who lost in the general election in a landslide. Many of those Democrats look at Bernie Sanders and see another such candidate, and think electing a Democrat is more important than complete agreement with the nominee's positions.
2. Popularity Overall - Many Democrats pay close attention to polling. In deciding which primary candidate to support for the Democratic nomination, they look to see which candidate appears to have the largest number of supporters nationwide. They also look at comparisons of candidates with potential Republican opponents. Hillary Clinton's poll numbers are excellent with Democratic voters across the spectrum and across the nation.
3. Name Recognition - Many people look closely to see which candidate is best known by Democratic voters. While that may seem to be an artificial way to decide whom to support, it's a real factor. A large number of Democrats who vote actually pay little attention to politics and vote based on factors many of us do not consider important. How well-known a general election candidate is has much to do with electability. That may be a bad thing, but it is a real thing.
4. Support by minority voting blocs - Black voters, Hispanic voters, Asian voters and other groups have increased in numbers over the years. Today, in several states with large delegations of electoral college votes, minority groups actually outnumber white voters. How they vote, and whether they vote may well make an enormous difference in the outcome of the general election. Poll numbers in these groups is often an important factor in deciding who to support.
5. Appeal to a majority of voters - Even for very progressive Democrats, it's easy to recognize that the votes of centrist and independent Americans are crucial to winning in any presidential election. In fact, those voters make up the largest single group of voters in those elections. A nominee who doesn't appeal to that group has little chance of winning, historically. So, it's an issue to consider.
6. Turnout - Turnout is a very important factor in election outcomes. Which candidate will result in the largest turnout of Democratic voters is something that needs to be considered in every presidential election year. Again, history is the guide, not just opinions of the candidates' positions. Not every candidate I like can create a massive turnout of Democrats.
Does the importance of these factors suck? Yes, probably. But they exist and affect the outcome of every election. For many Democrats with long histories of election activism, decisions about whom to support must take all of them into consideration. For many Democratic activist, electing Democrats to office is really the highest priority. If we fail in that, we simply fail. As we've seen, it's very easy for an election to result in a Republican being elected. That's a bad thing, so I'm working to prevent that, if I can.
Who do I support? I support Senator Sanders in the primary race. I'll be caucusing for him in Minnesota on March 1. Do I think he will be the nominee? Not really, but the primaries are where I support candidates who best match my positions. If too few others vote as I do, someone else, probably Hillary Clinton, will be the nominee. She's a Democrat, too. I can heartily support her in the general election and will refrain from attacking her during the primaries. If she's the nominee, I'll be supporting her enthusiastically, as I do all Democratic general election candidates. Nothing I say now will come back to haunt me later. I'm a realist and don't burn my bridges during the primaries.
= new reply since forum marked as read
He's my best choice and that's the man I'm going to vote for. 
is to look at head-to-head polls between a potential Democratic nominee against potential Republicans.
If supporters can prove their candidate would perform better in a general election match up via scientific polls, then they have a case.
I don't think that works. I'm comfortable with letting them screw things up all on their own. 
Who knows, probably some Gore, Kerry, Dean, (fill in the blank) fans out there. I like Mr. Sanders but I think if either he or Ms. Clinton are elected we will have a repeat of the McConnell's strategy to make it a "failed presidency. I would prefer to have someone in the office that not only is in our party but would not act as a personal lightening rod for the ire of the (re)Pukes. 
Showing just how much he supports Senator Sanders.
only occasionally are exposed. When they are, a lot of people are surprised. What is sometimes revealed is not attractive, to say the least. You have lots of support here, too.
