The federal government shut down for the second time in three weeks Friday, driven to the brink by acute congressional dysfunction and pushed over it by the objections of a single conservative senator. The partial shutdown began just after midnight when the government, operating on the latest in a series of short-term spending bills, ran out of money because Congress missed its deadline to pass a new one. But the closure could be brief, with minimal disruptions to federal workers and others. The Senate was expected to pass a massive spending deal in the early morning hours Friday that would reopen the government. The legislation would then head to the House, but the outlook there was less certain because of opposition from liberal Democrats and conservative Republicans, and quick passage was not assured.