Nancy Pelosi, put away that tape measure! That seems to be the conventional wisdom the day after a key congressional election in San Diego. And it may even be correct–that is, Pelosi should not assume she will be picking out new curtains for the House Speaker’s office following this fall’s elections. In felonious Duke Cunningham’s district, another Republican, former Representative Brian Bilbray, was able to hold the seat for the GOP, beating back the Democrat 49 to 45 percent. If the Ds cannot pick up a seat when an R is nabbed on bribery charges and tossed into prison, that’s a sign that the “culture of corruption” charge (see Jack Abramoff) they are campaigning upon may not do the trick in November. (Representative William Jefferson, a Democrat accused of taking $100,000 bribe, is sure not helping on this front.) Cunningham’s district was a Republican area. But to regain the House, the Dems need to do well in heretofore GOP districts.

Without reading too much into the results of one race, there is good reason for Democrats to worry: illegal immigration. Bilbray hyped his support for tough border enforcement, siding with the House Republicans’ keep-’em-out/toss-’em-out approach and attacking the Bush-favored Senate compromise position that blends a (convoluted) path-to-citizenship with steps to beef up the border. And that might have won him the race. During the campaign, Bilbray called for building a fence “from the Pacific Ocean to the Gulf of Mexico.” Celebrating his victory, Bilbray said, “The president proposing amnesty was absolutely a big problem. In fact, it wasn’t until I was able to highlight the fact that I did not agree with my friends in the Senate or my friend in the White House on amnesty that you really saw the polls start supporting me strongly.”

Now nervous-Nelly Republicans have a test-case to apply to their own races. If it’s a good fit for the district, Republican candidates will surely sound the illegal immigrant alarm to drive base-voters to the voting booth. Many were probably planning to do this already. Bilbray is proof it works.

When Latinos were out in the streets weeks ago to protest the House Republicans’ harsh immigration bill, there was talk among commentators about the rising political clout of Hispanic-American voters. But rallies do not make voting patterns. And that clout may not arrive quick enough to help Democrats in five months. Historically, it takes a long time for new voting blocs to vote. Over the years, the greatest predictor of whether someone will vote in an election has been whether they voted in the previous one. Even if Americans of Latin American origin are enraged by conservative Republicans, that anger may not register at the polls (particularly in an off-year election) for some time.

On the other mano, conservative voters pissed off about the trumped-up crisis of illegal immigration are already accustomed to expressing their outrage on election day. It may well be that it is not to the GOP’s advantage to make illegal immigration a national issue in the election. (The Wall-only approach divides the party, puts off business supporters, and might alienate moderate voters.) But in many a district, bashing illegal immigrants will serve the party well. In these spots, if the choice of targets for voter are either a corrupt party controlling Congress or illegal immigrants sneaking into America to steal jobs, commit crimes, alter the culture, and perhaps engage in terrorist acts, guess who wins.

This week, Senate Republicans tried to play the gay-marriage card–and they failed to defeat a Democrat-led filibuster. But they did throw a chewed-up bone to their social conservative supporters. Congressional Republicans also intend to wave the flag-burning issue soon. It’s possible these hot-button wedge issues don’t juice up Republican-leaning voters as much as they used to. But illegal immigrants may trump gays and flag-burners as Enemy No. 1 for the GOPers this year. In some districts–maybe critical districts–Jack Abramoff will be no match for that.