There is now more than a theoretical chance that Hillary Clinton may not be the Democratic nominee for president...

The inevitability behind Mrs. Clinton's nomination will be in large measure eviscerated if she loses the June 7 California primary to Bernie Sanders. That could well happen...

Another problem: In recent weeks the perception that Mrs. Clinton would be the strongest candidate against Donald Trump has evaporated. The Real Clear Politics polling average has Mrs. Clinton in a statistical tie with Mr. Trump, and recent surveys from ABC News/Washington Post and Fox News show her two and three points behind him, respectively.

Then there is that other crack in the argument for Mrs. Clinton's inevitability: Bernie Sanders consistently runs stronger than she does against Mr. Trump nationally, beating him by about 10 points in a number of recent surveys.

Mrs. Clinton also faces growing legal problems. The State Department inspector general's recent report on Mrs. Clinton's use of a private email server while she was secretary of state made it abundantly clear that she broke rules and has been far from forthright in her public statements. The damning findings buttressed concerns within the party that Mrs. Clinton and her aides may not get through the government's investigation without a finding of culpability somewhere.

With Mrs. Clinton reportedly soon to be interviewed by the FBI, suggesting that the investigation is winding up, a definitive ruling by the attorney general could be issued before the July 25 Democratic convention in Philadelphia. Given the inspector general's report, a clean bill of health from the Justice Department is unlikely.

Finally, with Mrs. Clinton's negative rating nearly as high as Donald Trump's, and with voters not trusting her by a ratio of 4 to 1, Democrats face an unnerving possibility.