Don't know if the US report should be completely trusted. A few things certain: China built the great firewal; it can do much more than that. Given the pressures it put on ISPs and Google like to give away details of dissidents, no doubt similar pressures can exist against Governments.
"US easy target for Chinese cyber-spies, says report " (25 November 2008)
For the report itself, see US Congress report especially p. 291 et s.
Thus that the two former candidates to the White House may have been targeted by CHina, is far from impossible. "Obama, McCain Cyber-attacks have Chinese Origins?" (17 November 2008)
"China denies hacking US politicians' computers" (ZDNet.uk, 13 June 2008)