Flip-flopping can easily derail a presidential campaign. John Kerry's infamous line on the Iraq war — "I voted for it before I voted against it" — solidified his image as a politician who would take almost any position if it would get him elected. He never overcame it.

Similarly, Mitt Romney's rapidly changing positions on abortion, health care, gun control, global warming, and taxes made him the king of the flip-flop. PolitiFact even created a Flip-O-Meter to keep track of his statements.

Of course, all presidential candidates — including the successful ones — modify their positions on key issues to appeal to the broadest range voters. Sometimes candidates even legitimately change their minds. But when taken to an extreme, flip-flopping can dramatically undermine a presidential campaign. The term flip-flop has existed since the late 1800s, but it's become one of the deadliest charges in politics.

That's why it's so fascinating to watch the transformation of Hillary Clinton. In recent weeks, she has changed her positions on several key issues quite dramatically.

Clinton's call for an "end to the era of mass incarceration" in the wake of the Baltimore riots was a direct rebuff of criminal justice policies enacted during her husband's presidency. Her bold promise to expand President Obama's controversial executive actions on immigration reverse the ambivalence she showed during the 2008 campaign when asked in a primary debate if undocumented immigrants should be allowed to have driver's licenses. And her embrace of same-sex marriage came even though she once supported the Defense of Marriage Act, one of the most high-profile anti-gay pieces of legislation ever enacted.

All of this led former Bush speechwriter David Frum to remark, "At this point we have to wonder, which if any policies of the Bill Clinton administration does Hillary Clinton still endorse?"

That's a good question. But this one is perhaps more important: Are these really flip-flops — or signs of a candidate naturally evolving as times change?

Hillary Clinton has been a national political figure for a really long time. It makes sense that she has changed her mind. Haven't you changed your mind on many things since 1992? Does anyone really hold the same position for decades on end?

And do we really want a president who never changes her mind?

Now, there is another side to this. Maybe Clinton's changing positions really do evidence her lack of character. Are they a sign that she has no clear convictions — that she's willing to say whatever, be whomever, and do whatever is necessary to win?

We're still 18 months from the 2016 election. But how these questions are answered may determine if Hillary Clinton becomes our first female president, or whether she's destined to be inducted into the flip-flopper's hall of fame.