My National Post column describes why the Tea Party has caused Republicans to lose elections that seemed well within their grasp.

The Obama-Romney contest will get the eyeballs, but the more important battle Tuesday night will be the battle for control of Congress.

Today, Republicans control the House of Representatives 242-193. Democrats hold the Senate, 53-47 (including two independents who caucus with the Democrats, Joe Lieberman of Connecticut and Bernie Sanders of Vermont).

Most House-watchers expect the Republicans to lose seats, but not enough to forfeit control. The mid-range scenario projects losses of between seven and 11 for the GOP. Losses on that scale would not jeopardize Republican control. They would, however, imply the defeat of almost all the more moderate conservatives in the Republican caucus. If Barack Obama wins reelection, he’ll meet a House even more hostile and intransigent than the House that nearly pushed the United States into default on its obligations in the summer of 2011.

The Senate outlook is even grimmer for Republicans. Earlier in the year, Republicans hoped they might win both the presidency and the Senate, restoring their post-9/11 united control of all three elected branches of government. Now it seems more probable that the Democrats will expand their Senate majority, most likely by picking up Republican-held Senate seats in Massachusetts and Indiana, and holding once seemingly vulnerable Democratic seats in Virginia and Missouri.

How? Why?

The short answer is: The Tea Party struck again.

Indiana, for example, should have been an easy Republican hold. One of the most Republican states outside the South, Indiana has elected only three Democrats to the U.S. Senate since World War II, two of them the father-and-son succession of Birch Bayh and Evan Bayh. The seat open in 2012 had been held by Richard Lugar, a senator best known for his work to secure loose Soviet-era nuclear materials. Lugar won his last race, in 2006, with 87% of the vote.

But Lugar was growing old and—worse—had cooperated too much with President Obama. A Tea Party Republican named Richard Mourdock launched a primary challenge against Lugar and won. Mourdock then proceeded to share his ideas with the broader Indiana electorate, including this one: “I came to realize that life is that gift from God. And, I think, even when life begins in that horrible situation of rape, that it is something that God intended to happen.”

Those words were pronounced in the heat of a televised debate. Mourdock later clarified that he did not mean to say that rape is intended by God; only that rape-caused pregnancies are intended by God. The clarification did not help, to say the least, and Mourdock now badly trails his conservative Democratic opponent.

Mourdock was not the only Republican candidate to expatiate on the subject of rape.

Read the entire column at the National Post.