As the horsetrading winds down, it's clear that Elizabeth Warren is the right choice to head the new consumer financial services protection agency. Will she be given the chance?

Ms. Warren’s climactic hour begins now: three years after she hatched the idea for the agency, the White House has backed it, the House of Representatives has approved it and it is a top Democratic priority in the Senate.

Many fans, including Representative Barney Frank, Democrat of Massachusetts, hope Ms. Warren will run it. But even if the agency is approved, it might be far weaker than what she envisioned, thanks to fierce opposition from the financial industry.

Critics argue that such an agency, which would regulate mortgages, credit cards and nearly all other loans to consumers, would tighten credit in an already tight market, stifle innovation and hurt small businesses.

They have another objection as well: to Ms. Warren herself. As one administration official acknowledged, the prospect of her running the new agency may be an impediment to its creation because of her crusading style, her seemingly visceral loathing of financial services companies and her expansive way of interpreting assignments.

“ ‘Loose cannon’ would be an appropriate term to apply in her case,” said Dean Baker, co-director of the Center for Economic and Policy Research and a Warren supporter.