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Since 1968, except for the anomaly of the Carter presidency in the middle 1970's and the Clinton years, it's been GOP all the way, at least in the White House. Congress started going to the GOP in the mid-1990's with the House. And, as Glenn says, the GOP and the Blue Dog wing of the Dems dominated in the Senate. For all the love of Bill Clinton, he certainly didn't dominate politically.
You might want to compare that history (40 years) with the stretch in the 19th and early 20th century. There, except for two split presidencies of Grover Cleveland and then Woodrow Wilson, it was GOP from Grant through Hoover! In fact, the only times of real Democratic dominance were during FDR-Truman and Kennedy-Johnson. Wilson was a lame duck in his last two years (and ill to boot), and Truman had to contend with a strong GOP in Congress.
The election of 2008 will be a watershed, similar to 1932. The country is divided, but they want action -- which they cannot get with a GOP president, as Congress will remain in Democratic Party hands. The people know it's time to act. For all McCain's abilities to "reach across the aisle," a split between White House and Congress will mean dithering and doodling.
Should Obama win, it will also mean a watershed for the Supreme Court. The older liberal judges will be replaced by new liberal judges, and the slow dead squeeze on the court will stop. Maybe Scalia will have a stroke. We can only hope.