One best-case scenario for Jeb Bush's candidacy looks like this: George W. Bush's legacy softens substantially from the record-low ratings he "enjoyed" once he left office. Voters decide that Jeb's relationship with his brother is not a big deal and maybe even a positive.

And lo, new polling from CNN/ORC and Bloomberg/Des Moines Register gives us two indicators that this scenario is coming true.

George W. Bush is now viewed more favorably than Hillary Clinton, and his favorability trumps President Obama's approval.

And, in Iowa  at least, Republicans largely view George W. Bush as an asset to his brother.

We've noted before that sluggish approval ratings for  Obama were bad news for Clinton. There's a correlation between the president's approval rating and how well the person from his party hoping to be his replacement does in November.

But this Dubyaissance may not be the unalloyed good for Jeb Bush that it may seem. First of all, it's worth remembering that Obama's job approval and his favorability are different. The latter tends to be higher than the former (at least comparing CNN polling with Gallup), likely since they measure slightly different but related things.

More importantly, there's a factor that could complicate the idea (to the extent that it exists) that W. might be an asset to Jeb: That other Clinton.

Comparing favorability for the three most recent presidents and Hillary Clinton, George W. Bush still beats Obama and Hillary. But Bill beats them all.

And that Bloomberg/DMR poll asked about him, too.

This is just Iowa and just within the party. But Clinton is viewed much more positively.

Hillary Clinton's approval rating, it's been noted, has dropped significantly since her time as secretary of state. This isn't a surprise; we've noted before that those numbers always sink during campaign season. (Also note that the CNN favorability numbers are better than a number of other recent polls, as compiled by HuffPost Pollster.)

But the same thing also happened to her husband! Notice his polling in 2008, while she was still in the hunt for the Democratic nomination. In part, that's due to his highly visible presence on the trail.

So here's George W. Bush's trend over time. It seems unlikely at this point that he'll hit the campaign trail, though he may work behind the scenes to bolster his brother's chances. But as the Republican nomination progresses, don't be surprised if those numbers start turning downward once again.

At the end of the day, George W. Bush might not be as big a drag on his brother as it may once have seemed. But in the ex-president family poker game, Hillary Clinton still has the ace. Which she'll need, if Obama's numbers don't improve.