When legislators no longer have the skills, interest or ability to gather the detailed information needed to hold executive-branch officials accountable, the power of the executive is left unchecked.

You've likely never heard of William Natcher, which would have been just fine with him. Natcher spent four decades in Congress representing the area around Bowling Green, Kentucky, and for the most part the national press ignored him, just as he ignored them. He didn't have time for burnishing his public image; he was what is known on Capitol Hill as "a work horse, not a show horse."

For many years, Natcher chaired a subcommittee of the House Appropriations Committee that dealt with the departments of Labor and Health and Human Services. In his day, the Appropriations subcommittee chairs were arguably the most powerful legislators on Capitol Hill: they were known as "the College of Cardinals" and were feared and respected not just by their colleagues, but, more importantly, by the people who ran the executive- branch departments they oversaw.

These days, the position carries much less power. As Scott Lilly, a longtime congressional staffer who now teaches at Georgetown University, put it recently in an insightful article for the congressional-affairs journal Extensions, the chairmen once known as the Cardinals are now "more like a rag tag band of parish priests."

I'm telling you this because what might seem like a bit of obscure congressional trivia is actually a key reason Congress is far less effective as an institution and why power has shifted to the executive branch. Congress may still oversee executive agencies, but not very well. The disappearance of legislators like Natcher is a big reason why.

Watching Bill Natcher at work was a lesson in what it means for Congress to be a co-equal branch of government. He prepared painstakingly for his subcommittee hearings - scrutinizing agency budgets, filling entire notebooks with questions and observations about executive-branch decisions, reaching out to the contacts he'd made over decades to understand the implications of the tiniest changes in policy, working closely with his Republican counterpart to examine every line in the budgets they oversaw.

He'd spend days grilling administration officials, making them explain their policies and holding them accountable for every dollar they'd spent and proposed to spend. He wasn't rude or impatient or partisan - officials of both parties knew they'd be treated courteously, but that when they came before him, they'd better know their budget and operations in detail and be able to justify every increase they were proposing.

Natcher wasn't alone. Most of his fellow Appropriations subcommittee chairs did this. They secured the information Congress needed to make informed decisions about the federal budget and government policies. And they put the executive branch on notice that Congress was watching its every move.

As Scott Lilly points out, various changes have undermined this role. The Republican caucus decided in the mid-1990s to limit its subcommittee chairs to six years. Being a member of Congress today requires endless fundraising and public relations, and affords far less time for committee business. The partisan environment stresses ideological point-scoring and downplays rigorous oversight. Congress now relies excessively on omnibus and supplemental bills. All this has shifted power to a distracted leadership and out of the hands of congressional experts who had the time and interest to oversee executive agencies.

Why does this matter? Because for all its faults, Congress is still the most representative institution our nation possesses, and therefore the place where tough oversight of the executive must occur.

The appropriations process, when the executive branch must ask for funding, is the strongest lever Congress controls to ensure that taxpayers' money is being spent effectively and that policy represents the interests of the American people. When legislators no longer have the skills, interest or ability to gather the detailed information they need to hold executive-branch officials accountable, Congress simply cannot do its job properly.

"We are dealing with a $10 billion black box," one frustrated congressional staffer told Lilly, lamenting how easy it has become for federal agencies to sidestep scrutiny from Capitol Hill. The power of the executive is going unchecked.

Lee Hamilton is Director of the Center on Congress at Indiana University. He was a member of the U.S. House of Representatives for 34 years. This column originally was published in 2012.