Lee Sang-deuk, the elder brother of President Lee Myung-bak, is to be summoned by prosecutors today for questioning in connection with the ongoing savings bank scandal.

Investigators have reportedly secured evidence suggesting that the former six-term lawmaker of the ruling Saenuri Party took hundreds of millions of won in bribes from Lim Seok, the disgraced chairman of Solomon Savings Bank, between 2008 and 2010. Solomon was suspended from operations in May due to capital shortages.

The president’s brother is also suspected of having received illicit money from Mirae Savings Bank, another suspended savings bank, and the Kolon Business Group, a second-tier chaebol group that he worked for before entering politics.

The summons indicates prosecutors have secured enough evidence to indict the powerful politician. Although Lee had been suspected of being involved in other scandals, prosecutors had never called him in; they just submitted written questions to Lee, allowing him to answer them in writing. This time, however, prosecutors are expected to seek an arrest warrant after questioning him.

Suspicions about Lee’s involvement in corruption have been raised since the early days of the incumbent government. As one of the core members of the president’s inner clique, he wielded enormous influence on the government ― so much so that it has long been said anything could be done if he supported it.

Specific corruption allegations against Lee surfaced last November when prosecutors investigated Lee Kook-chul, chairman of SLS Group. The businessman was found to have given several hundreds of millions of won to the former lawmaker’s aide to rescue his group from bankruptcy. Prosecutors found 700 million won in a bank account of the former lawmaker’s secretary.

Prior to that, Lee was alleged to have used his influence in arranging for Pohang University of Science and Technology to invest 50 billion won in Busan Savings Bank to help it raise capital in 2010.

Lee was also suspected of having taken money from Prime Savings Bank, while one of his aides was found to have received 150 million won from Jeil Savings Banks. The two troubled savings banks were suspended last September.

Prosecutors will have to thoroughly investigate these and other allegations involving the president’s sibling. They also need to probe other politicians, presidential aides and high-ranking officials at financial regulatory agencies who are alleged to have received money from the suspended savings banks.

The imminent downfall of the president’s brother is a poignant reminder of a chronic political problem in Korea ― the inability of the president to prevent his aides and relatives from engaging in corruption.

In the case of Chun Doo-hwan and Roh Tae-woo, many of their relatives and aides were indicted on corruption charges. The two presidents themselves committed corruption and served prison terms.

For Kim Young-sam and Kim Dae-jung, the main sources of their problems were their sons.

The late Roh Moo-hyun sought to break the unwholesome political tradition but his aides and his elder brother, Roh Gun-pyeong, betrayed his expectations and undermined his integrity.

Lee Sang-deuk should have learned a lesson from Roh Gun-pyeong. He probably thought he would be different. But he could end up convicted, just the same.

Lee should have left politics when his younger brother became a president. In early 2008, many advised him not to run for his sixth term in parliament.

But he rejected this advice, saying his political life would not be swayed by his family ties with the president. Yet lobbyists gathered around him, seeking to buy his personal clout. Now he has no one but himself to blame for the trouble he is in.

For President Lee, the prosecutors’ investigation into his elder brother must be truly embarrassing. Last October, he baffled his critics as well as advocates by describing his administration as “morally perfect.”

Since then, the president has seen some of his closest confidants, including Choi See-joong, former chairman of the Korea Communications Commission, and Park Young-joon, former vice minister of knowledge economy, arrested on charges of corruption.

The successive arrests of the president’s confidants illustrate the difficulty of fighting the deep-rooted culture of corruption stemming from nepotism and cronyism. One of the tasks facing the next government is to address this problem.