How does the congress check the acts of the president of the united states?

Question

I need three examples

Answer 1

The system is broken.  There aren't three examples that couldn't be run around by the Office of Legal Counsel, or as Dave87 says, just ignored.

Answer 2

The US attorney scandal is a good one. Bush fired all the US attorneys that wouldnt prosecute democrats- this is the Seigleman scandal.

So Congress investigates- tehy subpeona Harriet Miers, Rove and Josh Bolton- who ignored teh subpoenas, So congress went to the justice dept to compel these people to testify- and Bush's homeboy Mukasaky REFUSED TO ENFORCE THE SUBPEONAS

and thats how the system of checks and balances has broken down