But what happens if they do?
It could have been very different. Had Bernie Sanders won the caucuses in Iowa and Nevada, Hillary Clintonâ€™s campaign would now be in disarray. Rather than todayâ€™s South Carolina primary being a foretaste of the likely landslide sheâ€™ll win on Super Tuesday, it would be seen as a must-win vote simply to remain in the race; Super Tuesday itself would most likely have been a closer contest building off the back of a hat-trick of wins in the first three states, never mind the next two rounds with potential swing contests in Kansas, Nebraska and Michigan.
But he didnâ€™t. By a head in Nevada and a hairâ€™s breadth in Iowa, Clinton prevailed. By this time next week she will in all probability have a large lead in votes, states won and delegates pledged, the momentum will be with her and Sandersâ€™ challenge will be fading.
So, a straight run through to the nomination and the White House beyond? Barring accidents, yes to the former and probably to the latter â€“ particularly given Trumpâ€™s increasingly powerful grip on the GOP nomination. Except that an accident may occur, in the shape of the e-mail investigation.
The US law enforcement process is cumbersome and lengthy. Even if the FBI were to announce that it had a prosecutable case today, itâ€™s not impossible that a trial wouldnâ€™t occur until after November. All the same, we need to consider what would happen if they do come to that conclusion â€“ and the key question then is when they do so.
Before considering seven time periods that would generate different outcomes, letâ€™s first remember than Hillary may well choose to fight on anyway. Her ability to do so will vary depending on what evidence becomes public, as well as when (again), but everyone is innocent until proven otherwise and she can say that it is not for an FBI opinion to stop her, or anyone else, running for office. Whether the public agrees is another matter.
But putting that to one side, letâ€™s take a closer look at those timeframes if she is forced to pull out of the race.
1. Before late March
If Hillary withdraws while the March primaries are still ongoing, Sanders becomes the nominee. Itâ€™s too late now for any latecomer to file for entry to all but a handful of elections (California is the only sizable state left; its deadline is 26 March), and Sanders would sweep up enough delegates directly from the primaries and caucuses to assure himself of the nomination.
2. Between late-March and mid-April
By late-March, 55% of pledged Democrat delegates will have been elected. By the end of April, three-quarters have. This is the grey zone where Hillary will have locked up enough supporters to prevent Sanders from winning outright but doesnâ€™t have enough to dictate terms. Weâ€™re looking at a brokered convention here. Chances are that Sanders will have appeared out of the race prior to Hillaryâ€™s withdrawal so isnâ€™t automatically first-reserve. Instead, the party seniors would likely turn to someone seen as a safe pair of hands who already holds very senior office: Joe Biden is by far the most obvious candidate, with the added advantage that heâ€™s already flagged up his availability when he said that he regrets not running. There would still be the delegates to manage and Sanders would still no doubt maintain his bid but I suspect that the party would unite relatively quickly around Biden.
3. Between mid-April and the convention
At this stage, Hillary should have sown up enough delegates to hold an outright majority at the convention. Even if sheâ€™s forced to withdraw, sheâ€™d still be in a powerful position to recommend an alternative to her supporters (indeed, sheâ€™d be in a powerful position to keep running). Again, Biden becomes the natural alternative, given that Sanders will have fewer delegates of his own, but Hillaryâ€™s running mate â€“ if selected â€“ would be a possibility as well depending on experience and abilities.
4. Between the convention and the filing deadlines for November
Itâ€™d take something quite extraordinary for her to have to withdraw as so late a stage but if she did then thereâ€™d need to be an emergency appointment as candidate in her stead, and her running-mate would by this stage be the natural choice unless sheâ€™s seen to have really messed up earlier on that score (think Palin or Quayle).
5. Between the filing deadlines and the general election
This would be a horrible scenario and could well produce chaos (and for that reason, one would think the FBI would be very keen to avoid what would appear a direct intervention in the democratic process). But if it did, then her name is already on the ballots and the voters would have to go with that. In some states, the Electoral College members have discretion to choose someone else but in others theyâ€™re legally required to vote for the name on the paper. It probably wouldnâ€™t matter: the Republican would almost certainly win anyway.
6. Between the general election and the Electoral College vote
The public have cast their votes by this stage so Hillary is likely to have done much better than if sheâ€™d withdrawn prior to the general election. If sheâ€™d â€˜wonâ€™ on November 8 then the Electoral College members might be best all voting for her anyway as the alternative would be a constitutional nightmare, potentially putting Trump or Cruz into the White House after the voters picked Clinton, on the assumption that she would then decline to serve. Obviously, if she loses the public election then it doesnâ€™t matter what her Electors do.
7. Between the Electoral College vote and inauguration
Declining to serve might still be an option â€“ perhaps by refusing inauguration â€“ but the constitution gives little flexibility to Congress to interpret the Electorsâ€™ votes and a letter to Biden as President of the Senate requesting votes for her be set aside (for example) would be of doubtful constitutional value. More likely would be the process ending with her becoming president and resigning or being impeached.
Interesting though all this is, we shouldnâ€™t get too carried away. Whatever the evidence, the fact remains that the FBI has not yet acted and to do so now would result in them being accused of political bias unless they have a cast-iron case. The probability remains that we will see a perfectly normal route through to the nominations and elections. Even so, there still remains a small chance that the FBI find something from her past sufficient to start the legal ball rolling. As such, itâ€™s worth keeping some insurance on the relevant cover candidate at the right price. At the moment, I donâ€™t think the 33/1 for Biden as Democrat nominee is value but events can move quickly.