WASHINGTON — Senator Marco Rubio of Florida is leaning heavily toward running for re-election to the seat he swore he was giving up after six often frustrating years and a failed presidential run, associates said on Friday, a reversal that would upend one of the most competitive races in the country.

Mr. Rubio could make his decision public early next week after he spends the weekend with his family in Florida weighing the personal, political and financial considerations of another campaign. One adviser who described the senator as “all in” said Mr. Rubio’s staff members had already begun scouting a site for a possible announcement.

The likelihood of a re-election bid seemed to grow on Friday when one of Mr. Rubio’s potential rivals, Representative David Jolly, suddenly dropped out of the race and said he would seek another term in the House instead. Earlier in the day, Mr. Jolly foreshadowed his move, telling CNN, “Marco is saying he’s getting in.”

Ever restless, strategic and ambitious — and only 45 years old — Mr. Rubio has spent the past few weeks discussing with his friends and colleagues the difficulties he would face maintaining his political profile if he left the Senate. He would like to run for the presidency again, either in 2020 or 2024, and is concerned that his opportunities would be far more limited if he were no longer in office.