Obama has used agency regulations and executive orders to bypass Congress because he knew that Congress would not pass the measures he imposed unilaterally by executive orders and agency regulations.  Obama bragged about doing this by saying, "I've got a pen, and I've got a phone."

Bill Clinton's aide, Paul Begala, referred to this as "stroke of the pen 'Law of the land. Kind of cool."

To correct this, the Republican Congress plans to enact measures to limit the power of agencies to issue regulations.  The Washington Post reported on January 2, 2017:

GOP leaders have cited the 21-year old Congressional Review Act, which allows Congress to cast simple majority votes of disapproval for regulations, as a way to block anything the administration has ordered since June 2016.

… the CRA has been used only once. But in December, the conservative House Freedom Caucus began compiling a list of more than 200 regulations it views as vulnerable to a disapproval vote. They include "burdensome" school lunch standards, tobacco regulations, laws that set higher wages for contractors and elements of the Paris climate-change agreement[.] ...

Republicans intend to supplement the CRA by enacting a law that would subject any regulation with an economic impact greater than $100 million to a vote of Congress, a change that would have prevented nearly every climate or employment rule change of the Obama years. The measure, called the Regulations From the Executive in Need of Scrutiny Act, or Reins, is a conservative priority that passed the Republican House in 2011, 2013 and 2015[.] ... Republican aides now hope for a vote on Reins in the coming days so it can be sent for Trump's signature immediately after he is sworn in on Jan. 20.

Article 1, Section 1 of the Constitution states:

All legislative Powers herein granted shall be vested in a Congress of the United States, which shall consist of a Senate and a House of Representatives.

While this is clear, Congress created numerous agencies with the power to issue regulations to administer, interpret, and enforce laws.  For example, the IRS issues numerous regulations on the meaning of income, credits, and deductions.  The agencies have also been busy with Obamacare, issuing regulations such as those forcing the Little Sisters of the Poor to offer abortion coverage as part of their medical insurance.

The president has enormous power because he appoints the Cabinet and the heads of the agencies.  But voters have no check or balance on the actions of the agencies because while we elect Congress, we have no vote to select the agency chiefs.

An agency regulation can be rejected by a majority vote of Congress, but this rarely happens.  A regulation may also be challenged in federal court by an aggrieved party.  But the judicial standard to overturn a regulation favors the agency.  In Chevron, U.S.A., Inc. v. Natural Resources Defense Council, 467 U.S. 837 (1984), the Supreme Court  stated a two-step test for whether a court should defer to an agency's interpretation of the law: (1) did Congress directly address the precise question at issue?  And (2) if not, is the administrative agency's answer based on a reasonable construction of the statute?

This puts the burden of proof on the person challenging the regulation.  Most regulations are upheld by the courts, and most regulations are not challenged because it is expensive to litigate.

The result is that Congress has given away to agencies much of its power to legislate.  Congress passes a broadly worded statute and tells the agency to fill in the blanks.

The proposed congressional reforms to curb agency regulations are necessary to restore the balance of power between the president and Congress.

Even though we have a Republican president who may issue executive orders that we approve of, and appoint agency chiefs who would issue regulations that we favor, it is important to our federal system of separation of powers to restore the balance of power between the presidency and Congress.

One element of Obama's legacy will be that Congress restricts the power of the presidency because it was abused by Obama.