Former House Majority Leader Tom DeLay (R-Texas) on Wednesday warned Republicans not to underestimate Democrats this fall.

DeLay, fresh off having the Justice Department drop a federal investigation against him, said GOP wins in the midterm elections aren't "a given" due to the strength of the grassroots infrastructure Democrats built in 2006 and 2008.

"Over the last ten years, the Democrats, particularly the Democrats in the House, have put together one of the most powerful grassroots coalitions that I've ever seen," DeLay said during an appearance on Fox News. "So it's not a given that the Republicans are going to win all these seats this year, because the Democrats have had a grassroots organization to help stave off a lot of their losses."

DeLay was a top campaign strategist for Republicans during his time in office. He helped build up the GOP's infrastructure through a prolific fundraising machine and close alliances with grassroots conservative groups.

DeLay said it was "hypocritical" for Democrats to plead for money from donors when they were characterizing their efforts as cash-strapped, but warned fellow Republicans not to discount Democrats' ground game.

"It helped them win in 2006 and in 2008," he said. "And it's a new campaign paradigm, where they go in with grassroots people, go door to door, canvass the entire district and pump in unlimited amounts of money."