Crossroads GPS up with ads in five key Senate races

The Republican-allied, deep-pocketed American Crossroads is up with another major television buy, hitting Democratic candidates in five key Senate races: Massachusetts, Montana, Missouri, Virginia and Nebraska.

The new buys will run for two weeks and total $1.8 million. Each is an attack tailored toward the particular candidate and state, with the Massachusetts ad slamming Harvard Prof. Elizabeth Warren for embracing the Occupy Wall Street protests and others seeking to tie incumbent Democratic Sens. Claire McCaskill (Mo.), Jon Tester (Mont.) and former Democratic National Committee Chairman Tim Kaine (Va.) to Washington and President Obama.

Warren's campaign responded quickly, sending out a fundraising appeal, telling supporters that they "need your help to fight back" against the ads and pointing out that former advisor to President George W. Bush (and Democratic bogeyman) Karl Rove is involved with the group.

Kaine's campaign fired back as well. "This ad proves what Virginians already learned during George Allen and Karl Rove’s disastrous tenure in Washington – they know nothing about cutting spending and balancing budgets, " said Kaine for Virginia spokeswoman Brandi Hoffine.

This is the second major ad buy in as many days for the group. They are also running $2.4 million worth of advertising attacking Obama in Ohio, Florida, Colorado, Pennsylvania and North Carolina, five other key swing states. The group avoided doubling up on ads in one state, likely so they don't clutter the airwaves with multiple messages.

Watch the Massachusetts ad here:

Watch the Virginia ad here:

This post was updated at 11:20 a.m.