US National Security Interests or "Let's Keep Out the Foreigners"?

Actions to stop non-US companies from acquiring US companies or doing business here are growing increasingly troublesome - note the blog posting from the VC world's Brad Feld on efforts to stop China's Lenovo from selling to the US government.

I'm all in favor of a secure US but we need some reasonable evidence before we do ourselves greater long-term economic harm. Other countries have used security and other "national interest" arguments in spades to block US and other companies from entering their markets. China did not invent this game - Japan had actively used national security grounds in the past, and I recall this line from my days in Korea in the late 1980's. Our own use of such reasons will only embolden protectionist measures elsewhere - though if there are real security threats, let's by all means get these out in the open for evaluation.