Has Obama Crossed the line? Some say yes, many times. The list of offenses include conducting war against Libya without Congressional authorization, unauthorized giving of taxpayer money to the International Monetary Fund despite laws specifically banning such actions, unilateral executive actions, circumventing Congressional oversight and the Senate confirmation process through appointments of special "czars" and "recess" appointments, and even targeted assassinations of American citizens.
The Canadian Free Press even did an article out-lining 50 specific offenses and crimes they considered to be grounds for impeachment. That was two and a half years ago. Since he's continued his violations of his oath of office, and abuses of power through numerous executive orders, obstructions of justice by stopping congressional oversights and inquiries, and ordering offensive military actions within other countries without declarations of war.
The last president to be impeached was done on the grounds of lying under oath. However, former President Clinton, nor any other president for that matter, has actually had an impeachment make it all the way through congress. In President Clinton's case, many believe the following congressional elections being dominated by democrats was due to a national backlash against this impeachment attempt.
When I attended a town hall meeting for Pete Sessions, in Garland, TX earlier last year, Pete himself claimed he was the reason why the GOP controlled house was not pursuing impeachment of Obama stating, "I want to win the election". However, even after the election and more controversy over Obama's executive orders targeted at guns, only unrealized threats of impeachment have been seen.
Once again today, we are in much of the same situation. While the house very likely could be convinced to impeach Obama, they likely won't because it would be seen as a futile attempt, knowing the votes simply aren't there in the Senate to confirm the guilt of President Obama. Maybe in a couple of years there will be, but by then Obama's tenure as President will be quickly coming to an end; or at least many of us hope so.