The war, now in its seventh month, has killed more than 34,000 Palestinians, according to Gaza health authorities
Senators will question Rousseff in a session expected to last all day. They are then due to vote late on Tuesday or early Wednesday on whether to convict Rousseff and remove her from office.
If she is dismissed, interim President Michel Temer would officially take over as Brazil's leader to serve out the remainder of the presidential term through 2018.