Paul Ryan
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In the first official sign that the Democratic Party is starting to worry about Paul Ryan's selection as vice president, the Democratic Congressional Campaign Committee sent out a fundraising email Monday urging donations in light of the supersized crowds, which reportedly reached as many as 15,000 in North Carolina. 
The email, from DCCC field director Brynne Craig, is entitled "disturbing report" and cites a Wall Street Journal piece of the crowd sizes (emphasis added):
I just got this disturbing report: Yesterday’s Romney-Ryan rally in North Carolina pulled in an overflow crowd of 15,000 people.

There’s no spinning that number. It’s a LOT of people, and the Republican base is energized.

And that’s not all. Since the VP announcement, Romney’s campaign has brought in over 70,000 donations from his Tea Party base.

We’ve got to step up our game and mobilize our supporters -- starting right now.

Donate $3 or right now to help us rally our base around President Obama’s agenda >>
On Saturday immediately after the pick, the DCCC had sent around a fundraising email that sounded almost giddy about the Ryan selection. From the email:
Yeah -- THAT Paul Ryan. The architect of the Republican plan to kill Medicare. [...]
These next hours are critical. We need to contact key voters immediately and make sure they know about the Romney-Ryan plan to put millionaire tax cuts over Medicare for seniors.