Regarding line item veto, it DID pass in 1996. And then it was declared unconstitutional. Line item veto is a great idea...in theory. However, it has just as much potential for abuse as it does good use. Without the line item veto, the executive has to work with the legislature in creating the law. With the line item veto, the executive's power begins to dwarf the legislature. Without it, the legislature passes a bill that has parts the president doesn't agree with, then the president either chooses to sign into law what the majority of 535 elected representatives voted in favor of, or decides to veto the bill and send it back to the legislature with notes about his objections. If the elected representatives REALLY want this bill to become law, they can override the veto. This is often not the case and, instead, they must work with the executive for compromise. This helps to maintain the balance of power. Now, with the line item veto, the legislature passes a bill and sends it to the president - let's say it's a health care reform bill that is generally a good thing - and then the president gets to decide "you know what? I don't like this stuff about federal funding for abortions, and I don't like this stuff about scientific research that can help fight things like diabetes because it involves the injection of a human chromosome into mice" so he line item vetoes those important sections and signs the rest of the bill into law, giving the legislature no realistic opportunity to fight for those parts of the bill.
Yes, pork is a big problem, but the line item veto is not the answer. An executive that doesn't feel above working with the legislature and a more attentive and demanding public is. Bush wants a line item veto because he sees the real possibility that the Republicans may lose control of the legislature in 2006, and he wants a more powerful executive to fight that. Ask yourself: do you really want Bush to have even MORE power than he already has? Even if you're for Bush, picture the situation reversed. The line item veto upsets the delicate balance of power between the two branches.
As for the genetic research issue, there's an interesting (and admittedly quite biased) blog entry regarding that here:
http://scienceblogs.com/pharyngula/2..._antimanim.php