All the major news organizations released national polls last week to set baselines before the national parties hold their conventions.

Here's a quick summary:

Washington Post-ABC News: Obama 49%, McCain 45%

Fox News: Obama 42%, McCain 39%

Wall Street Journal-NBC News: Obama 45%, McCain 42%

New York Times-CBS News: Obama 45%, McCain 42%

Reuters/Zogby: McCain 46%, Obama 41%

GWU Battleground Poll: McCain 40%, Obama 39%

Finally, we have one poll that is focused just on 19 "battleground" states:

National Public Radio: Obama 46%, McCain 45% 

The next wave of national polls should come after this week's Democratic National Convention to measure the size of Obama's bounce.

At this point in the presidential campaign, it's hard to put much weight in the various national polls that come out every week. However, I think it will be very interesting to see if Sen. Barack Obama's trip to the Middle East gives him a bump. Conventional wisdom suggests the trip has been a roaring success so far.

The first national survey to come out since Obama left on his international tour will be released tonight at 6:30 by NBC News and the Wall Street Journal.

Update: The poll is now out and shows no bounce.

According to recent polls, Sen. Barack Obama is doing extremely well in states that have voted Republican in recent presidential elections.

• Montana: Bush won by 11 points in 2004, Obama leading McCain by 5 points
• Colorado: Bush +4, Obama +5
• Virginia: Bush +8, Obama +2
• New Mexico: Bush +1, Obama +3
• Florida: Bush +5, Obama +2
• Indiana: Bush +20, Obama +1
• Georgia: Bush +16, McCain +1
• Mississippi: Bush +20, McCain +4
• Alaska: Bush +26, McCain +4
• North Carolina: Bush +13, McCain +4

Also see:

• Is Obama a typical politician?
• Who is Barack Obama?

While many think it's too early to pay much attention to national polls at this point in the presidential race, it will be very interesting to see how much of a "bounce" Sen. Barack Obama received now that he's wrapped up the Democratic presidential nomination. The strength and longevity of an Obama bounce could be an early indicator of his chances in the general election.

Early tracking polls from Gallup and Rasmussen already show Obama getting an initial bounce. As Obama is increasingly portrayed in the media as the Democratic nominee, conventional wisdom suggests his bounce will increase his national lead over Sen. John McCain into the double-digits. However, if it's less, it suggests Obama may have lingering problems from the tough Democratic primary contests.

First Read argues the bounce is important for Obama because "it will determine the strength of his hand regarding Clinton as veep. If his bounce is tiny and his lead over McCain remains in single digits, there will be a lot of whispers from pro-Hillary circles that he needs her constituency. If Obama's bounce pushes his national poll lead into double digits, then he can more easily dismiss the idea of adding Clinton to the ticket."

Meanwhile, Dick Morris suggests Clinton could actually still replace Obama on the ticket: "If Obama makes a mistake and begins to drop in the polls or some other tape comes out or a new pastor emerges with more racial rhetoric, Hillary still has her 1,639.5 delegates. Count on her to back Obama in public, but look for her aides and supporters, and perhaps her husband, to raise the question of whether or not the results of the primaries should not be revisited in light of the trouble in the Obama candidacy."

In the next couple hours, we'll probably see leaked exit polls from Indiana and North Carolina. It would be wise not to pay much attention to them.

It's hard enough to poll primary races due to selection bias. However, several factors unique to today's election could throw off turnout models and make these survey's very unreliable:

• Overall turnout today is set to break historic records.
• The excitement of the race could change the number of late day voters who are never captured in exit polls.
  
• With open primaries in each state, large numbers of Republicans and/or independents are voting in the Democratic primaries.
• Voters participating in Rush Limbaugh's "Operation Chaos" may not tell pollsters the truth.
  
• Historical patterns don't mean much since it's been a very long time since presidential primaries in either state mattered very much.

If you really want to see some data, you're better off looking at Charles Franklin's final analysis of the primary polling.

With dozens of new polls out every week, it's tempting to use polling averages -- such as those used by Real Clear Politics -- to smooth out the many results and hopefully make them more understandable.

But as I noted several months ago on Political Wire, there are many reasons poll averaging doesn't work:

• Surveys are in the field at different times -- often over several days -- so respondents are not always aware of the same recent events.
  
• Each poll typically uses different methodologies for forecasting turnout. 
• Polls have different sample sizes, yet when they're averaged they are usually are weighted the same.
  
• Pollsters use different screens to determine likely voters.
  
• Some pollsters use telephone surveys while others use robocall surveys.
  
• The wording of questions on surveys can differ which can wildly skew results.
• Some of the pollsters included in the polling averages are just not reliable.
  

While doing a simple average can eliminate some of the biases noted above, the technique may also magnify them dramatically. As a result, the polling average can be more unreliable than the original polls themselves.