Let me give you some concrete examples.
President Obama has made close to 20 changes by now in his own Obamacare law passed exclusively by his own Democrats in Congress. He has done that by decree, without any authorization in the law, and in violation of the Constitution. The Constitution requires him to take care that the laws be faithfully executed, which means the laws as passed by Congress, and as he himself has signed into law.
The law as passed mandates both employers and workers to buy health insurance (workers when their employers don’t). The law as enacted says those mandates both become effective as of January 1, 2014.