Venetoclax and Ibrutinib in Treating Patients With Chronic or Small Lymphocytic Leukemia

Inclusion Criteria: * Patients with a diagnosis of CLL/SLL: * Cohort 1: Refractory to and/or relapsed after at least one prior therapy will be eligible * Cohort 2: Untreated patients with high-risk features (del(17p), or mutated TP53, or del(11q), or unmutated IGHV, or \>= 65 years of age) are eligible (cohort 2) provided they have active disease requiring treatment as defined by the International Working Group for CLL (IWCLL) * Eastern Cooperative Oncology Group (ECOG) performance status =\< 2 * Total bilirubin =\< 1.5 x upper limit of normal (ULN) or =\< 3 x ULN for patients with Gilbert's disease (in patients \[pts\] with elevated total bilirubin due to increased indirect bilirubin, pts with direct bilirubin =\< 1.5 x ULN are eligible) * Creatinine clearance \> 50 mL/min (calculated according to institutional standards or using Cockcroft-Gault, Modification of Diet in Renal Disease \[MDRD\], or Chronic Kidney Disease Epidemiology Collaboration \[CKD-EPI\] formula) * Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) =\< 3.0 x ULN, unless clearly due to disease involvement * Platelet count of greater than 20,000/mul, with no platelet transfusion in 2 weeks prior to registration; this criteria is waived if the thrombocytopenia is due to bone marrow involvement with the disease * Women of childbearing potential must have a negative serum or urine beta human chorionic gonadotropin (beta-hCG) pregnancy test result within 7 days prior to the first dose of …