US President Barack Obama delivers a statement after the Supreme Court left in place a lower court ruling blocking his plan to spare millions of illegal immigrants from deportation and give them work permits, at the White House in Washington, US, June 23, 2016. [Photo/Agencies]

WASHINGTON - The Supreme Court on Thursday dealt President Barack Obama a harsh defeat by blocking his plan to spare millions of illegal immigrants from deportation in a split 4-4 ruling that was a setback for his attempts to bypass the Republican-led Congress.

The ruling, coming seven months before Obama's term in office ends, marked the latest success that his Republican adversaries have had in thwarting a major policy initiative of the Democratic president. It also guarantees that immigration will remain a prominent part of the campaign ahead of the Nov. 8 election in which voters will pick his successor.

The 4-4 decision left in place a 2015 lower-court ruling blocking the plan, which was never implemented.

Obama's 2014 plan was tailored to let roughly 4 million people - those who have lived illegally in the United States at least since 2010, have no criminal record and have children who are US citizens or lawful permanent residents - get into a program that shields them from deportation and supplies work permits.

Obama's plan was blocked by lower courts and never went into effect. It was immediately challenged in court by Republican-governed Texas and 26 other states that argued that Obama exceeded his presidential powers by taking the executive action and bypassing Congress

The court, with four conservative justices and four liberals, appeared divided along ideological lines during oral arguments on April 18.

The 4-4 ruling constituted one sentence saying the court was equally divided with no written opinions. The split was possible because there are only eight justices following February's death of conservative Antonin Scalia.