Early this year, when things in America started to go bad for the Democrats — most dramatically with the Republican win in a Senate by-election in Massachusetts — they were able to console themselves with the thought that there was still plenty of time before the mid-terms to turn it around: time for the economy to improve, for Barack Obama to work his rhetorical magic, and for voters to rediscover some of the unpleasant aspects of the Republicans.

But no longer. Mid-term congressional elections are less than seven weeks away, and the GOP is clear favorite to take back control of the House of Representatives — analyst Nate Silver gives them about two chances in three. So all eyes were on this week’s final round of primaries to see if candidate selection could give a late boost to one side or the other in some crucial states.

The news when it came was good for the “tea party”, the radical anti-establishment insurgency within the Republican Party. Tea partier Christine O’Donnell, on the back of an endorsement by Sarah Palin, dispatched long-time congressman Michael Castle to win the senate nomination in Delaware, and another anti-establishment candidate won the nomination for governor of New York. In New Hampshire, after an excruciatingly slow count, the establishment’s Kelly Ayotte narrowly held off a tea party challenger to win endorsement for the seat of retiring Republican senator Judd Gregg.

For the Republicans, tea party victories are very much a mixed blessing. On the one hand, they indicate grassroots enthusiasm of the sort the party badly needs. Mid-term elections attract low turnouts (primaries, of course, lower still), and a committed base is critical for victory. On the other hand, tea party candidates tend to be extremists who provide plenty of ammunition for their opponents and risk hurting the party electorally. As Democrat senator Robert Menendez put it: “The fact that these individuals may play well in an overall Republican universe doesn’t mean they will play well in a general election universe.”

This is the big question for November: will turnout be high enough, and reach far enough into the uncommitted mainstream, for the increasing weirdness of the Republicans to start to outweigh their greater enthusiasm?

The tea party is affecting the GOP in more ways than just candidate selection. By showing the appeal — at least within the activist base — of certain themes, it is dragging more mainstream Republican figures towards the right, and therefore framing the party’s strategy more and more in extremist terms.

Hence Newt Gingrich, former speaker of the House and a possible presidential candidate in 2012, earlier this week painted Obama as fundamentally un-American, “outside our comprehension” with his “Kenyan, anti-colonial behavior”. This is becoming a common Republican theme, portraying Democrats (and Obama in particular) as outsiders responsible for all the woes of “real America” — what the New York Times calls “a general portrayal of otherness based on his age and ideology, his upbringing and, inescapably, his race”.

American voters have already rejected this approach once, when they decisively elected Obama in 2008 in spite of their country’s tortured racial legacy. But dissatisfaction with the economy and the lower mid-term turnout — plus the absence of the unpopular George W Bush — may well combine to reverse that verdict.

How much that would matter is an open question. An equally dramatic reversal in 1994 did not stop Bill Clinton from comfortably winning re-election two years later. But it did give Republicans control of the House for 12 years, and significant influence on policy that persisted whether or not they held the White House.

If Democrats want to prevent that from happening again, they’re running out of time to do something about it.