The 2010 primary season is under way, which at the congressional and gubernatorial levels is often no more than a quiet backwater in America’s electoral process.

In recent years, only a few such incumbents have lost their bids for renomination, and only a handful more have had to break a sweat.

No sitting U.S. senator or governor has lost a primary bid since 2006 — when Democratic Sen. Joe Lieberman of Connecticut and Republican Gov. Frank Murkowski of Alaska were both defeated. Meanwhile, just two House members were denied renomination in 2006. In 2008, there were only four.

But this year could be dramatically different. Distaste with government is palpable. In last month’s first-in-the-nation primary in Illinois, Democratic Gov. Pat Quinn came within 10,000 votes of losing his party’s gubernatorial primary. This week in Texas, Republican Gov. Rick Perry won renomination by making the Washington experience of his principal rival, Sen. Kay Bailey Hutchison, more odious to GOP primary voters than his own long run in Austin.

To be sure, no House incumbents were defeated in either Illinois or Texas, or for that matter, were even closely contested. But by modern standards, it would still be quite noteworthy if even six or seven House members, and a senator and governor or two, were beaten over the course of the primary season.

Several basic questions flow from all this: How high, really, will the level of anti-incumbent sentiment be in 2010? Will it be aimed almost exclusively at the Washington-ruling Democrats or will it envelop a significant number of Republican officeholders as well? Or might it play out on a piecemeal basis — in favor of a populist outsider such as Sen. Scott Brown, and against an experienced Washington hand such as Sen. Hutchison?

Primary voters over the course of the next few months will help provide answers, which should better define the true nature of the political landscape heading toward November.

In historical terms, the number of memorable primary seasons has been limited.

First to mind is 1938, when President Franklin D. Roosevelt tried unsuccessfully to purge powerful conservative congressional Democrats from the New Deal coalition.

Then there is 1946, a major transitional year in American politics immediately after World War II. Eighteen House incumbents were beaten in primaries, while a slew of others led by John F. Kennedy and Richard Nixon made their first steps onto the political ladder by winning their party’s congressional nomination and ultimately a seat in the House of Representatives.

And finally there is 1992, when the combination of redistricting and the House banking scandal lashed at the Democrats and served as a precursor of the anti-incumbent tide that would rout them from Congress two years later. Altogether, 19 House members were beaten in the primary season of 1992, a post-World War II record. Fourteen of them were Democrats.

In recent decades, only the years that end with “2” routinely see much primary action on the House side. That is when the lines have been redrawn following the decennial census and incumbents are forced to take in new terrain that that they have not been representing. Some even find themselves paired against each other in the same district.

After that, House members tend to settle in for the rest of the decade, at least in terms of the primaries. And by the time the election year rolls around that ends with “0,” the political scene is usually quite placid. In 2000, just three congressional incumbents lost renomination bids. In 1990, it was just one.