If the Conservatives needed any reminding that they are in for a tough fight in Rochester and Strood, UKIP's historic breakthrough in Clacton was a painful reminder that what lies ahead is going to be one their most challenging electoral battles.
It was not so much that UKIP won but that it won so decisively, with a huge landslide for Douglas Carswell. Not only that but it came pretty close to dislodging Labour from what was supposed to be a safe seat - a result likely to induce some panic in the party's ranks.
No wonder that UKIP swiftly announced that its leader and first MP are heading down to Rochester tomorrow to give Mark Reckless a campaign boost and exploit its win for all it is worth.
For the Conservatives and Labour, the challenge is how to arrest the momentum UKIP appears to have and stop Mark Reckless crossing the finishing line first.
Up until now, the Conservatives have been relatively optimistic that while the contest would be close, they would be well-positioned to win and see off UKIP once it had its campaign is up and running. That view is no longer tenable or realistic and the least surprising consequence of last night's result is that bookmakers have now installed UKIP odds on to win Rochester and Strood.
The key problem for the Conservatives - and Labour - is that UKIP continues to attract support from those disillusioned with mainstream parties and politicans and there is arguably no better platform to register this disaffection than at a by-election. Of course, with increasing numbers of local councillors and MEPs and now an MP, this may change but it won't before voters go to the polls next month.
It is debatable whether David Cameron insistence that Rochester and Strood is now a vital battle is helpful. The refrain is clearly designed to encourage Conservative activists and supporters to get on the front foot but it raises the stakes for his own leadership.
The fact that the party has yet to select a candidate has not and is not helping. The plan for a postal primary, in which every constituent (even Mark Reckless) would have a say in who it should be as part of an "inclusve" process was initially attractive.
But the downside is that process is taking time and I just can't see it making much of a difference when voters go to the polls.
It will be another week before the party has someone in place, leaving UKIP to continue to make the running. I wonder now whether the party might regret its strategy but it is too late to do anything abouot it now.
Has the pendulum swung decisively towards UKIP in Rochester and Strood? The Conservatives will be kickstarting their campaign and are bringing in their heavy artillery to do what it can but will it be enough? As to Labour, the Heywood result suggests that it haemorrhaged support to UKIP and it continues to lack credibility over issues such as immigration, which cost it badly in 2010.
UKIP started from a position of thinking it had an outside chance of winning the by-election; now it believes it really can.