MEDELLÍN, Colombia — Álvaro Uribe, a powerful former president of Colombia, said Tuesday that he was resigning from his Senate seat after the Supreme Court disclosed that it was widening a criminal investigation of him to include accusations of bribery.
In a statement posted on Twitter, Mr. Uribe said that the investigation had left him “morally impeded to be a senator” and that he was leaving Congress to prepare his defense.
La Corte Suprema me llama a indagatoria, no me oyeron previamente, me siento moralmente impedido para ser senador, enviaré mi carta de renuncia para que mi defensa no interfiera con las tareas del Senado
— Álvaro Uribe Vélez (@AlvaroUribeVel) July 24, 2018
In Colombia, the resignation was an abrupt setback for a resilient politician who has dominated the country for two decades. Mr. Uribe served as president from 2002 to 2010, waged a pitched battle against his successor, founded his own party and continued on in the Senate as one of the country’s most popular politicians.
His star was ascendant again when a little-known candidate he backed in elections, Iván Duque, won the presidency by a large margin in June and pledged to restore Mr. Uribe’s legacy. The two men had also proposed a new judicial structure that would eliminate the Supreme Court, which was investigating the Uribe case.
The resignation threw Mr. Uribe’s comeback into question on Tuesday.
“It’s an issue that, without doubt, affects the party and changes the rules of the game for this political coalition,” said Pedro Medellín, a political scientist who writes a column for Colombian newspapers.
Some analysts said it also might give Colombia’s new president, who takes office on Aug. 7, the chance to govern outside of the influence of his popular patron.
“Duque is way more moderate than most of his party, including Uribe,” said Adam Isacson, an analyst at the Washington Office on Latin America, a human rights group. “Having Uribe out of the picture makes Duque less dependent on hard-liners in order to govern.”
While Mr. Uribe has been accused of many crimes related to Colombia’s long civil conflict, which left more than 220,000 people dead, none until now were known to lead to his resignation from any office.
But recent cases have put more pressure on the former president and his circle. In addition to investigations of Mr. Uribe and his associates, Mr. Uribe’s brother Santiago is also expected to face trial related to allegations that he ran a death squad on his ranch called the Twelve Apostles.
On Tuesday, the Supreme Court said that it would investigate Álvaro Uribe and Álvaro Prada, another senator from his party, for “the crimes of bribery and procedural fraud” that, according to the accusation, took place this year and were related to witness tampering.
The case stems from an earlier attempt by Iván Cepeda, a left-wing senator who has often sparred with Mr. Uribe, to investigate allegations that Mr. Uribe founded a death squad in his home province, Antioquia, before he became president.
Mr. Cepeda published a book on the subject. Mr. Uribe claimed that witnesses received money for their interviews, and he accused Mr. Cepeda of witness tampering.
In February, the Supreme Court dismissed the case against Mr. Cepeda and said it was opening an investigation into Mr. Uribe for witness tampering. The tables were now turned against the former president.
Some witnesses in the cases against Mr. Uribe and his associates have been killed in recent years in crimes that remain unsolved.
On Tuesday, Mr. Uribe’s allies rallied around the former president, while his rivals unleashed new attacks against him.
“The resignation of Álvaro Uribe is to evade the investigation,” Gustavo Petro, a left-wing senator who lost to Mr. Duque in the presidential race, wrote on Twitter.
Mr. Uribe posted attacks against the court on social media sites on Tuesday, saying that it had rushed to judgment and had ignored him. He accused one of its justices of leaking the decision to journalists and demanded his resignation.
Mr. Uribe has a long history of attacking the court. As president, he sued one of its justices for slander; went on a radio show to accuse another of trying to frame him for crimes; and was embarrassed by a wide-ranging scandal in which his government ordered wiretaps on the court and its investigators.
But having resigned from the Senate, his attacks on judges may be blunted, Mr. Isacson, the analyst, said.
“It’s very healthy for Colombia’s justice system not to weather daily attacks from a popular politician,” said Mr. Isacson of Mr. Uribe’s decision to leave his post while he was under investigation.