Bernie Sanders' religious beliefs should not be used against him to try and make a political point. All residents of the United States are allowed to practice whatever religion they choose. While Sanders should not attempt to force his beliefs on others and possibly should not have dragged that into his political agenda, DNC officials should be above getting involved in petty disputes with former candidates.
Ideally religion should play no role in deciding who gets to hold office. The entire world needs competent people in government, not religious ones. The DNC official was absolutely wrong in bringing Sanders' religious beliefs into the equation. That was uncalled for and a sign of weakness on the part of that official.
There was no justification. This is because our country is traditionally Judeo-Christian anyway, Although some Americans might not vote for a Jewish candidate, it doesn't mean the DNC should undermine him. They should have given him the same treatment as they gave Hillary. But Hillary is an insider with them.
The DNC should be absolutely ashamed of how they biased the primaries toward Clinton. The committee is only supposed to be the voice of the voters, but instead, they were doing everything they could to sway the elections. It's especially appalling that they wanted to use Sanders' religion against him.