He’s going after Cheney first because he doesn’t want Cheney to become president after Bush is impeached. It’s a ridiculous waste of time since it isn’t going anywhere. They will not get the votes necessary to impeach Cheney:

A veteran United States politician has introduced legislation urging Vice-President Dick Cheney’s impeachment for allegedly manipulating intelligence used to justify the US invasion of Iraq.
House of Representatives Democrat Dennis Kucinich introduced a resolution saying that Mr Cheney “has purposely manipulated the intelligence process to deceive the citizens and Congress of the United States”.
Mr Kucinich, a contender for the 2008 Democratic presidential nomination, said Mr Cheney did so “by fabricating a threat of Iraqi weapons of mass destruction to justify the use of the United States Armed Forces against the nation of Iraq”.
His Bill further accused the Vice-President of trumping up “an alleged relationship between Iraq and al-Qaeda,” and having “openly threatened aggression against the Republic of Iran absent any real threat to the United States”.

We live in interesting times when a member of Congress would attempt to impeach the Vice-President during a time of war.