Here’s how the Tea Party hurt the Republican party in the US Senate. The Tea Party candidates won in both Florida and Alaska, but they unseated moderate Republicans (Crist in Florida and Murkowski in Alaska), who would have won anyway.
However, the Tea Party cost the Republicans in Delaware (O’Donnell) and in Nevada (Angle), where
any other moderate Republicans, caucusing with the Republicans, would have easily won. Two seats in a 49-51 Senate is control of the Senate.
The Tea Party helped the Republicans win local, district elections and take the House, but cost the Republicans in some larger, statewide races in the Senate, including two key victories in Delaware and Nevada, and perhaps ultimately control of the Senate.
(I write this with Alaska, Hawaii, Washington, and Colorado still undecided.)