Gustavo Petro's left wing block tops the senate elections.
The right wing Democratic Center party edges ahead in preliminary results.
The elections set the stage for the upcoming presidential vote in May.
Strategic angle: Preliminary results show President Gustavo Petro's left wing block leading in the senate.
Gustavo Petro's left wing block tops the senate elections.
The right wing Democratic Center party edges ahead in preliminary results.
The elections set the stage for the upcoming presidential vote in May.