The convention bounce may not be extinct. But it's definitely on vacation.

It's still way too early to say anything definitive, but the limited numbers we have seen since last week's Republican National Convention show Mitt Romney managing a small — and in most cases statistically insignificant — bounce.

History shows that presidential candidates, and particularly challengers, generally see a bump up in the polls in the aftermath of their parties' conventions. Three or four days of what has generally amounted to a near-monopoly on the political news cycle will tend to do that.

But at this early stage, there's little evidence to think the GOP convention made a sizable difference. And that probably shouldn't surprise anyone.

As we noted on our Election 2012 blog Monday, a new Gallup poll shows nearly as many people came away from the Republican festivities in Tampa saying they were less likely to vote for Romney (38 percent) as saying they were more likely (40 percent). That's a smaller margin than any convention in at least the last three decades; most nominees have come away from the convention with significantly more voters saying they are more likely to vote for that candidate than they were before.

In addition, the 38 percent of people who rated Romney's acceptance speech as either "good" or "excellent" was lower than any nominee since at least 1996 — the last year for which Gallup data are available.

A look at the anecdotal evidence in key states, though, shows Romney is in slightly better position than he was before the convention.

Democratic automated pollster Public Policy Polling over the weekend released polls in four key states — Colorado, Florida, Michigan and North Carolina. And in all four, the numbers are slightly better for Romney than the last time PPP polled there a month ago.

In Colorado, Romney's six-point deficit from early August is now a three-point deficit. In Michigan, Romney is down seven points after being down by 14 in late July. And in North Carolina, Obama's three-point advantage from early August is gone, and the race is now a dead heat at 48 percent apiece.

Romney's favorable rating also improved by two points in Colorado, seven points in Michigan and five points in North Carolina.

In Florida, PPP shows the ballot holding steady at 48 percent for Obama and 47 percent for Romney. However, Romney's favorable rating did rise slightly, from 46 percent to 49 percent.

In each of these states, we should note, these changes are within the margin of error and thus shouldn't be over-interpreted. The movement is in the right direction for Romney, but it's hardly a game-changer and could disappear just as quickly.

In addition, it's hard to ascribe the gains totally to the convention. After all, even before the convention, swing state polls were showing Romney gaining slightly. PPP last polled in these four states about a month ago, and Romney could have made these small gains before the convention even took place.

So basically, we're waiting for more conclusive data.

In the end, though, it shouldn't be surprising if Romney gets little or no bounce. We live in a polarized political system right now in which the vast, vast majority of people have already made up their mind about who they're voting for. The universe of persuadable voters is just so small that basically all of the shifts are going to be within the margin of error.

In addition, the days of huge convention bounces might well be over. While 10 of the last 13 post-convention Gallup polls showed significantly more voters saying they were now more likely to vote for that convention's nominee, the three where that has not been the case all occurred in the last decade (Romney's 2012 convention, John McCain's 2008 convention and George W. Bush's 2004 convention).

Even Obama's much-hyped 2008 convention ranks on the low end as far as convention bounces go. And are we really expecting the already-cemented opinions of Obama to change much after the Democratic convention this week?

The fact today is that nobody has a monopoly on the news cycle. Even the coverage of Romney's and Paul Ryan's speeches was colored by fact-checking, distractions (Clint Eastwood, anyone?) and Democratic pushback. And that will be the case again this week.

This may just be the new normal. While past nominees have managed much more significant bounces, that probably just wasn't realistic for Romney or Obama this year. The best each could probably hope for is a few points on the margins.

The limited polling we're seeing suggests that Romney might be getting some of that. But we're still waiting on something more conclusive.

And sizable convention bounces may simply be a thing of the past.