Did Mitt Romney get a bounce by selecting conservative darling Rep. Paul Ryan (R-Wis.) as his running mate? It depends on how you define "bounce," says Christian Heinze at The Hill. He's raised $7 million, and "the new energy evident everywhere [at his campaign events] has been priceless." Both of those are "bounces — one financial, the other rabbit-like." But when it comes to polls, there's no bounce to be found. Gallup reports that in the first four days of the Romney-Ryan ticket, Romney gained a statistically insignificant 1 point, putting him ahead of President Obama 47 percent to 45 percent. That matches other polls, says Gallup's Jeffrey M. Jones, suggesting "a generally tepid reaction to the Ryan pick, especially in comparison to past vice-presidential choices." Why hasn't Ryan given Romney the traditional post-VP-announcement bump? Here, five theories:

1. Ryan was a relatively unpopular pick
One reason for Ryan's "below-par bounce," says Nate Silver in The New York Times, is that his "favorability ratings are fairly low by the standard of recent vice-presidential nominees." And no wonder: His best known accomplishment, a proposed budget that radically transforms Medicare, is tremendously unpopular, say Douglas E. Schoen and Jessica Tarlov in The Daily Beast. If he wants some love in the polls, "Romney may have no choice but to distance himself from some of Ryan's views." What he can't dodge, say Chris Cillizza and Aaron Blake at The Washington Post, is that Ryan is "a 14-year veteran of Congress," the least popular institution in America. 

2. Few people know who Ryan is
Romney's insignificant bounce is historically unusual but not that surprising since Ryan isn't well-known, says Nate Cohn in The New Republic. Voters are still learning about the congressman and his policies. And since Ryan is such a blank slate, it's especially "imperative for both sides to define him early." For what it's worth, Romney pollster Neil Newhouse favors the "he's a relative unknown" explanation.

3. Today's relentless news cycle mutes poll swings
It may be unfair to compare the tiny post-Ryan bounce to those produced by previous veep contenders, says Doug Mataconis in Outside the Beltway. Today's "world of round-the-clock political coverage means that it's that much harder for a campaign to change the narrative of the race in a news cycle that never really ends."

4. The bounce is still coming
On the other hand, says The New York Times' Silver, Romney's Ryan "announcement was made on a Saturday — a slow point in the news cycle" and it was further marginalized by competition from the final days of the Olympic Games. Since voters are still digesting the news, "I can't rule out the possibility that, a few days from now, we'll be talking about a significant bounce" for Romney. In fact, "the data suggest the possibility that Romney may get a delayed bounce," says Gallup's Jones. He performed better in the last two days of the rolling four-day poll than in the first two.

5. There are very few undecided voters out there
Perhaps the best explanation for Ryan's failure to bounce is that "nothing has really moved polls this cycle," says The Hill's Christian Heinze. Not the gaffes, round-the-clock campaigning, nor the "massive spending on TV ads." So maybe this has nothing to do with Ryan and everything to do with this "enormously partisan moment, where about 90 percent of voters have picked their candidate, no matter what." In this environment, it's likely that we just won't "see big bounces, at any point, even after the conventions."