Congressional leaders can be forgiven for not sharing their 2008 presidential candidates’ enthusiasm for the White House. The reason is simple: Successful pursuit of the presidency has meant failure for the majority party in Congress. Presidents Bill Clinton and George W. Bush both saw their parties lose Congressional majorities. Both presidencies broke the long-standing trend where parties’ Congressional fortunes waxed and waned with presidential elections. This development has great implications for the White House, Congress and country alike. At a time of rising policy challenges at home and around the world, the nation sees its political system shrinking from the tasks.

The long-standing trend in American politics is for the party winning the presidency to see its numbers in Congress increase in that election and then reverse during the following midterm election, when the president’s party loses seats. This pattern has created a flow and ebb to U.S. politics.

This peak-and-valley pattern has been amazingly consistent. Over the past 70 years, 27 of the 35 elections have conformed to it. However, of the eight nonconforming elections, five occurred in just the past 14 years. The numbers involved underscore the trend’s importance. From 1938 through 1990, the party winning the White House gained a net average of 15.6 House and 1.4 Senate seats and then lost 31 House and 3.8 Senate seats in the following midterm election.

From 1992 on, the pattern essentially reversed to a tails-you-win-heads-I-lose proposition for the president’s party in Congress. Since Clinton’s election, the party winning the White House has averaged a net loss of .75 Senate and 1.5 House seats, and coupled this with an average loss of 3.5 Senate and 17.8 House seats in the following midterm election. Their president’s election has not only not given the party a boost, but also the midterm losses have continued cutting into their legislative base, essentially dissipating, not invigorating, the Congressional party and flipping control of Congress in both administrations.

The breaking of this electoral trend has helped produce the longest period of partisan balance in either the Senate or House’s history. Over the past 14 years, the difference between majority and minority status in both chambers has averaged just over 5 percent — a shift of three Senate and 12 House seats being enough to change a chamber’s control on average.

The effect on presidents has been no less significant. Neither Clinton nor Bush took office with anything resembling a mandate. Even when election did not result in his party controlling Congress, a president able to point to a seat gain could claim endorsement of his platform. For the past two administrations, just the opposite occurred. The opposition had little reason to cooperate, being electorally energized to resist the president — particularly when midterm elections offer even greater opportunity.

If this trend continues, it could result in a permanent lame-duck president: assuming office weakened, enduring a midterm electoral hit and then immediately beginning the campaigning for the next presidential election. Congress’ current partisan near-balance exacerbates this because no majority has sufficient cushion to withstand it and each minority sees the majority within reach.

Such a development could not come at a worse time. The Bush tax cuts expire after 2010 with rates dramatically increasing, and the alternative minimum tax will affect 52 million taxpayers in 2015 if unaddressed — with repeal costing $670 billion over 10 years. On the spending side, baby boomers will begin retiring next year, setting off a spending surge that will increase Social Security’s growth rate by 50 percent over the next 10 years. Coupled with Medicare and Medicaid, these three entitlement programs will increase 124 percent to 11 percent of the gross domestic product by 2017.

Equally daunting challenges await in foreign policy. It is a certainty that the next president will take office with troops in Afghanistan and Iraq. A realistic assessment will require that they remain for part or all of the next president’s term. And the contagion of conflict threatens to spread farther into Iran and Syria, with Israel and Palestine as perpetual potential flashpoints. The Mideast is not the only problem area. North Korea and Venezuela both threaten their own regions as well as the limits of America’s military resources. Nor do all of our international challenges involve military conflict, as increased global concern on environmental and market access issues demonstrate. Finally, as the Sept. 11, 2001, terrorist attacks remind us, unforeseen threats and problems will emerge to join the list.

Such an overload of challenges encourages failure. While they create demands, narrow Congressional majorities deny a president the means to address them. And even success on one or two challenges will leave many unanswered, so that the list of accomplishments falls far short of the to-do list.

The tale of recent elections is successful presidential candidates receiving the rose and their Congressional parties grasping its thorns. The cost of the presidency has become Congress, but it is a cost that Congressional parties don’t pay alone. Presidents arrive with miniscule mandates and reduced legislative resources.

It is just the opposite from Franklin D. Roosevelt’s presidency, when large majorities enabled large challenges to be addressed and still allowed the weathering of midterm losses. While today’s mounting challenges do not yet meet those faced by FDR in 1933, they do represent a watershed that will fundamentally change America. They also present potentially severe crises if not properly handled. With these coming challenges, which are singly enough to sink any White House, the last thing America’s presidents need is an electoral undercurrent running against them.

J.T. Young served in the Treasury Department and the Office of Management and Budget from 2001 to 2004 and as a Congressional staff member from 1987 to 2000.