But this is a snapshot, a photograph of the moment. You have to go to the videotape to see the bad news for Clinton.
Here's the full favorability trend for Clinton since her husband first started winning primaries in 1992.
You can see she's had highs and lows, including a spike in her net favorability in the late 1990s (thanks to a certain Ms. Lewinsky) and again when she became secretary of state in 2009. But you can also see that the bubble of support she enjoyed as secretary of state has deflated a lot.
Let's focus in on the net approval rating.
After that flurry of Gallup polling when she was a candidate in 2008, Clinton's net approval kept rising and rising. Then, as she walked away from the State Department, it kept falling and falling. It's about as low now as it was before she took that job -- precisely the wrong sort of momentum a presidential candidate wants to see.
If we focus in on the other metric, those with no opinion, we see something else.
It's often the case that people don't go from loving to hating a political candidate. "No opinion" (or, in other contexts, "don't know") can serve as a waystation between the two, a place for those who supported a candidate to land before saying that they now oppose them. There is a lot of squishiness here (figures are rounded, polling is often far apart), but the last two Gallup surveys have seen a jump in those offering no opinion. How can you have no opinion of Hillary Clinton, a person who has been in the public eye longer than some people who are old enough to drink have been alive? Because your opinion has changed. (Notice the similar increase in "no opinion" when her net favorability dropped at the start of her time as senator.)
The odds are good that Clinton's favorability will stabilize as the campaign begins/gears up. Clinton had better hope it does. And she should probably also hope that people who aren't sure how they feel about her get back on board. At least until next November.