Campaign spending on radio and television advertising has crossed the half-billion-dollar mark.

With the $37 million being spent this week on political advertising -- including the campaigns and the Super PACs that support them -- the grand total for this campaign is now more than $512 million, about the amount spent on advertising in the entire 2008 general election, according to an NBC News/Smart Media Group Delta analysis.

Almost half of that money is coming from outside groups, like Super PACs -- and the vast majority of the outside money is going to support presumptive Republican nominee Mitt Romney.

Outside groups have spent a whopping $238 million on the 2012 general-election campaign. And about $9 out of every $10 – in total, $205 million – spent by an outside group is going to support Romney or hammer President Obama.

By contrast, outside groups supporting Obama have spent $33 million, accounting for 14 percent of the total ad spending on the incumbent president’s behalf, including efforts by Obama’s own campaign.

Put another way, just 25 percent of all the ads that are intended to benefit Romney have come from the former Massachusetts governor’s campaign; outside groups, including super PACs, have made up the difference. By contrast, 86 percent of the total advertising effort meant to boost Obama has come from the president’s own campaign.

But Obama’s campaign is still far and away the largest-single spender, checking in at $207 million.

Crossroads is the second-biggest spender at $105 million -- $59 million from Crossroads GPS, a 501(c)4, and $46 million from the Super PAC American Crossroads.

The Romney campaign comes in third at just $67 million. But with outside groups’ help, Romney and his supporters -- or Team Romney -- are outspending President Obama and his allies -- Team Obama -- $273 million to $239 million.

For the past month, Team Romney has outspent Team Obama by nearly 2-to-1. But that margin is up to 2.5-to-1 this week -- with Team Romney outspending Team Obama $25.8 million to $11.1 million.

Part of that is the Romney campaign is almost on par with the Obama campaign this week. The Romney campaign is spending $8.4 million to the Obama camp’s $9.9 million.

Previously, outside groups had to spend just to get Team Romney at the same level as Team Obama.

2012 AD SPENDING

Team Romney: $273 million

Team Obama: $239 million

Total: $512 million

OUTSIDE MONEY

Pro-Romney: $205 million (86% of all outside money going to boost Romney)

Pro-Obama: $33 million (14% of all outside money going to boost Obama)

Total: $238 million (47% of all money spent on ads this general election)

% FROM OUTSIDE GROUPS

Team Romney: 75% (of Team Romney’s ads are from outside groups)

Team Obama: 14%

Or…

HOW MUCH OF THE ADS SIDING WITH ONE CANDIDATE OR THE OTHER ARE COMING FROM THE CAMPAIGNS?

Romney: 25%

Obama: 86%

AD SPENDING BY GROUP

Obama campaign $207 million

Romney campaign $67 million

Crossroads $105 million (GPS $59 million, American $46 million)

Americans for Prosperity $42 million

Restore Our Future $29 million

Priorities USA $28 million

RNC $15.5 million

Concerned Women of America $4.8 million

American Future Fund $4.5 million

American Energy Alliance $3.2 million

SEIU $2.5 million

Planned Parenthood $1.5 million

Priorities/LCV $1 million

Move On $144,000

Numbers USA $115,000

Week of 8/13-8/19:

Team Romney $25.8 million

Team Obama $11.1 million

Total: $37 million