Because British and American politics are intertwined. Elections in the USA and Britain have forecasted electoral sentiment in the other country many times. I will not go into the historical precedents for my statements and leave that to you, dear reader.
The recent British election shows a fractured electorate and no clear majority. Does this sound familiar? The only difference in the US is a real third party has not emerged like the Liberal Democrats in the UK.
Voter discontent in the US could show up in gains for the Tea Party, Libertarians, and Independents, though those groups, with exception of the Independents are too small and not cohesive. The Independents are just that without any platform, leaders, or unifying force or issue so they cannot hold any kind of power in the US.
Should be an interesting mid-term election and look for the power-elite controlled media to keep painting any group other than the Dems or Pubs as fringe crazies who cannot govern.