GOP groups ride to rescue in 3 key Senate races
© Getty
Two of the largest outside groups defending the GOP majority in the Senate are dumping millions in late money into three close races just two weeks before Election Day.
The Senate Leadership Fund (SLC), a super PAC tied to the American Crossroads network of organizations, and the National Republican Senatorial Committee (NRSC) are spending big to defend embattled GOP incumbents in Missouri and North Carolina and to make a play for the open Nevada seat.
The NRSC began placing its own ads in Missouri Tuesday morning.
Both groups are also pouring late money into North Carolina, where Sen. Richard BurrRichard Mauze BurrGOP senators request interview with former DNC contractor to probe possible Ukraine ties North Carolina congressman says he won't seek reelection after redistricting Senate passes bipartisan bill to permanently fund historically black colleges MORE (R) is running just ahead of former state Rep. Deborah Ross (D). The SLC will pour $2.5 million into new ads defending Burr, while the NRSC has only begun making its purchases.
And the SLC is making a massive bet on Nevada, where Rep. Joe Heck (R) represents the GOP’s best shot at flipping a Democrat-held seat.
Over the next two weeks, the group will spend $4.7 million in the Las Vegas media market and another $3.6 million in the Reno market. 
That spending will dwarf Democratic spending on behalf of Cortez Masto. The Democratic Senatorial Campaign Committee will spend $1.7 million in Las Vegas and about $500,000 in Reno over the same time period.
Cortez Masto is also receiving help from unions like the AFSCME and the SEIU, the Senate Majority PAC and Planned Parenthood, which is running its own $760,000 ad blitz in Las Vegas.
All told, candidates and outside groups have spent more than $664 million on television advertising in the battle for control of the Senate. 
New Hampshire remains the most expensive fight in the nation; Democrats and Republicans have spent a combined $112 million there. The contest between Sen. Pat Toomey (R) and former state environmental chief Katie McGinty (D) in Pennsylvania has cost both sides a combined $110 million.
In Nevada, Heck and Cortez Masto have drawn a total of $82 million in total television spending.
Spending figures compiled by a Republican ad buyer watching the market shows Democrats have outspent Republicans in five states over the last month before Election Day — Indiana, Missouri, North Carolina, New Hampshire and Pennsylvania. Republicans own a spending advantage in Florida and Nevada.
Democrats need to flip five seats — or four if they retain the White House — to win back control of the Senate.