LONDON - European shares resumed their downward journey on Thursday after gains in the previous day, with investors dumping riskier assets on Moody's warning the United States may lose its top credit rating if lawmakers fail to hike the country's borrowing limit.At 0709 GMT, the FTSEurofirst 300 index of top European shares was down 0.7 percent at 1,091.05 points. It rose 0.7 percent on Wednesday after declines in the previous three straight sessions. The index is down 2.1 percent this week.Moody's said late on Wednesday it saw a rising possibility that the statutory US debt limit will not be raised on a timely basis, leading to a default on US Treasury debt obligations."US debt situation is annoying. It's politics pure and simple. I guess they'll get out of it in time so no harm will be done," said Koen De Leus, strategist at KBC Securities.